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Reference Book on Chemical Engineering v. 1

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Page 1: Reference Book on Chemical Engineering v. 1

• emlca

• • =n Ineelln

D.Sen

(f.U NEW AGE INTERNATIONAL PUBLISHERS

Page 2: Reference Book on Chemical Engineering v. 1

Reference Book on

Chemical Engineering

Page 3: Reference Book on Chemical Engineering v. 1

THIS PAGE ISBLANK

Page 4: Reference Book on Chemical Engineering v. 1

Reference Book on

Che ical Engineering

Volume I

D.Sea 8.Ch.E.

Fellow of Ill", Institution of Engineers (India) Former Listed 1081 Consultant , .. Retired Chief Engineer (Chern.)of BVFCl, (Formerly HFCl) Namrup Unit, Assam

NEW AGE INTERNATIONAL (P) UMITED, PUBUSHERS Now Delli, . B'"&,I",,, . Ch.nn,; • Cochin • G ...... h .. i • lIyd<n.b. d J.undh., • Kolkau • Luckll_ . Mumb.; • Ranch;

Page 5: Reference Book on Chemical Engineering v. 1

Copyright © 2005 New Age International (P) Ltd., PublishersPublished by New Age International (P) Ltd., Publishers

All rights reserved.

No part of this ebook may be reproduced in any form, by photostat, microfilm,xerography, or any other means, or incorporated into any information retrievalsystem, electronic or mechanical, without the written permission of the publisher.All inquiries should be emailed to [email protected]

ISBN (10) : 81-224-2331-0

ISBN (13) : 978-81-224-2331-0

PUBLISHING FOR ONE WORLD

NEW AGE INTERNATIONAL (P) LIMITED, PUBLISHERS4835/24, Ansari Road, Daryaganj, New Delhi - 110002Visit us at www.newagepublishers.com

Page 6: Reference Book on Chemical Engineering v. 1

'To My Mother

'Wlio lias takJn mucli interest in progress of the flooK-, the flooK-is adicatea

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PREFACE

A Chemical Engineer needs to know not only the im~ide changes in a Production Process viz. Chemical, Physical, Thermochemical, Thermodynamics and Kinetics, but also he has to know the basics of other engineering disciplines as well as current developments. During my long service period in Production, Process Design and Projects, I found most of these information are available at different sources and is not always possible to acquire these infonnation always. 'Ib meet these gaps, I have given as much information as possible in Volume I and Volume II of this book on various processes, data tables, some unit operations etc. usuany required by Professional Chemical Engineers and Chemical Engg. students. In addition, a chapter on Glossary of Terms has a]so been provided for refreshing the essential information un chemistry and other topics.

In preparation of this "Reference Book on Chemical Engineering" some senior engineers working in chemical industries have extended support in preparation of some chap~n;; ip parlicular 1 like to thank K. OM Ex. ED, KRIBHCO, Hazirll; D.K Roy, Ex. GM, Namrup Fertiliser Unit; KP. Sinha, ~r. Development Engineer, DCL, Professor U.P. Ganguly, Retired, Chern . Engg. Deptt. , Lr~T. Kharagpur had reviewed this book. The index for words had been provided. The author also likes to thank Ms. B. Sen for secretarial assistance in preparation of the manuscript..

Kolkata D.SEN

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CONTENTS

Preface (uii)

1. Fertilisers 1

2. Heat Transfer 25

3. Pulp and Paper 37

4. ehlor Alkali Industry 45

5. Cellulosic Fibres (Rayon) 50

6. Selected Process Equipment Design 63

7. Petroleum Refinery 70

8. Active Carbon 75

9. Refrigeration 78

10. Coal Tar Chemicals 96

11. Refractory Bricks 103

12. Explosives and Detonators 107

13. Water Treatment 111

14. Metal Cleaning Process 128

15. Mangane!!le Dioxide 130

16. Wind 'furbine for Power Generation 133

17. Centrifugal Pumps 13S

18. Industrial and Town Gases 143

19. LNG Production 159

20. Products Manufactured from Benzene, Ethyl Ben2ene,

Ethylene. Ethylene Oxide, Ethanol and Others 162

21. Synthetic Iron Oxide Pigment 167

22. Dyes, Intermediates and Dyeing 170

23. FlourCl;cent or Optical Whitening Agent (FWA) 172

24A. Flame Retardants, Halans, Fire AlarmsIHydrants and Rubber and Expanded Plastics 174

24B. Float Glass , Carbon Black, Electrophoresis, Dry Ice and Technological Development in Iron and Steel Industry and Electrolytic Chlorinator 179

25. Ceramic Colouring Materials 185

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(x)

26. Glass Fibres for Insulation and Other Uses 187

27. Plastics 190

28. Flocculation 195

29. Phosphoric Acid 198

30. Electroplating Process 207

3J. Couling Towers 212

32. Paints and Painting 217

33. Biogas Plant (Domestic Use) 223

34. Sugars 225

35. Phenols for Disinfection 230

36. Ferrous Alloys 232

37. High Carbon Charge Chrome 234

38. Characteristics of Valves Used in Chemical Process Industry 236 39. Boiler Feed Pumps and Standard Values for Boiler Feed

and Circulating Water 237

40. Crystallizer Classification 240

4J. Brief on Offshore Oil Exploration and Transportation Pipeline 242

42. Insecticide or Pesticide 243

43. Critical Path Method WPM) 254

44. Psychrometry 255 45. Glasses and Textile Glass Fibres 258

46. Environment and Pollution Air and Water 260

47. Vegetable Oil Refining 275

48. Furfural 282

49. Polyethylene Terephthalate Resin (Bottle Grade) 285

50. Process Evaluation of a Chemical Plant 288

51. Detail Project Cost Estimation 298

52. Types of Contract 307

53. Project Financial Management 309

54. ISO.90oo Series Quality Assurance System 320

55. Conversion Factors 328

Index 336

Page 12: Reference Book on Chemical Engineering v. 1

1. GENERAL INORGANIC FERTILISERSThese are plant nutrients which are grouped as nitrogenous, Phosphatic and mixed fertilisers

with or without potassium chloride (muriate of potash, MOP). Among nitrogenous fertilisers, ureacontaining 46–46.5% (wt) nitrogen is most important because of high nutrient content and is widelyproduced and used. Di-ammonium Phosphate (DAP) single super phosphate (SSP), mono ammoniumphosphate (MAP) and dicalcium phosphate (DCP) are common phosphatic fertilisers. CAN isAmmonium nitrate mixed with lime. Mixed fertilisers are balanced nutrients for plants as they containnitrogen, phosphorous and potash in various proportions. Fertilisers are generally termed as containingN : P2O5 : K2O or simple N : P : K where N stand for % nitrogen, phosphate as % P2O5 or simpleP and Potassic as % K2O or simple K. The ratio is % by wt.

Types of Inorganic Fertilisers

Type Constituents, % by wt Remarks

Nitrogenous Fertilisers use as prills and industrial

Urea, NH2CONH2 N = 46–46.5% Use as crystals or Prills

Ammonium Nitrate, N = 34.5% Explosives and fertiliser use

NH4NO3

UAN soln. N = 20% or NH3 = 23% UAN is urea mixed with ammoniumnitrate

Nitrolime or CAN N = 25% Mix. of 60% amm. nitrate and 40%lime stone (CaCO3)

Ammonium Sulphate, N = 21% Fertiliser use(NH4)2SO4

Phosphatic and Potassic:

Monoammonium Phosphate N = 11%, P2O5 = 52% Fertiliser useMAP (NH4H2PO4H2O)

Diammonium N = 18%, P2O5 = 46% Fertiliser usePhosphate, DAP or 21% = N, 53.5% = P2O5(NH4)2HPO4H2O

1

1Chapter

FERTILISERS

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2 REFERENCE BOOK ON CHEMICAL ENGINEERING

Dicalcium Phosphate, P2O5 = 51% Fertiliser use(CaHPO)4Single Super Phosphate P2O5 = 16–18% Fertiliser use

(Mixture of mono calcium

phosphate and Gypsum)

Tripple Super Phosphate P2O5 = 46–48%TSP (mix of tricalciumphosphate and Gypsum)

Liquid spray fertilizer (i) 24% AqNH3 soln. Fertiliser use

Developed after (ii ) Ammonia nitrate or urea(1950 in USA) aq. soln with liquid NH3

upto 50%

(iii ) Non press. Appln 32%aq. soln of urea and ammon.nitrate

Mixed Fertilisers

N P K 15 : 15 : 15 Fertiliser use

12 : 12 : 12

8 : 8 : 8

N P 18 : 46

16 : 20

20 : 20

N P K (other type) 17 : 17 : 17 Fertiliser use

10 : 22 : 26

14 : 28 : 14

19 : 19 : 19

N P K (foliar grades) 12 : 4 : 6 Foliar spray

6 : 12 : 6

5 : 8 : 10

Controlled release urea aldehyde Slow release to soil

fertiliser

2. BY DANGER CRITERIA, THERE ARE FOUR TYPES OF FERTILISERA type explosive fertilisers, exm. Ammonium nitrate-storage conditions are stringent.

B type fertilisers are self-sustaining progressive thermal decomposition.

C and D type fertilisers are not self-sustaining as well as do not subject to progressive thermaldecomposition.

Group B fertilizers are more important for storage.

Page 14: Reference Book on Chemical Engineering v. 1

FERTILISERS 3

3. RAW MATERIALS FOR FERTILIZERS PRODUCTION

Nitrogenous FertilisersFor manufacture of nitrogenous fertilizers, ammonia as intermediate product, is manufactured

first.

Raw MaterialsNatural gas (N.G) containing mainly methane and other higher hydrocarbon stock. (LSHS) is

also used where natural gas is not available. Other oil refinery distillation product like Naptha is alsoused as starting raw material although it is costlier. Even low sulphur and low ash bituminous coalis used in some plant (South Africa) as raw material.

Process Steps(i) These involve production of raw gas (CO + H2) with pre or post desulphurisation depending

on type of raw material used. For N.G, pre-disulphurisation is carried out first followed by steam-air reforming (two stage) using compressed air and compressed natural gas. H.P. steam generationfrom reformed gas (R.G.), H.T. CO conversion and L.T CO conversion for generation of equivalentH2 from CO, CO2 gases in the raw gas are absorbed in a CO2 absorber using pot. Carbonate withanticorrosion chemicals viz V2O5 or As2 O3 or using MEA/DEA absorption for CO2 followed bymethanation to convert residual CO and CO2 to methane. CO2 from CO2 absorbing solution isrecovered in a desorption tower using heat for regeneration of CO2. The byproduct CO2 from CO2desorption tower, containing over 96% CO2, is sent to urea plant for production of urea. Thesynthesis gas obtained after methanation and having H2 and N2 in 3 : 1 molor ratio, is used forammonia synthesis and compressed to 200–250 Kg/Cm2g and synthesized to produce ammonia inthe H.P ammonia reactor with recycle in the synthesis loop having synthesis gas compressor withrecycle gas circulator, primary and secondary condensation using cooling water and ammoniarefrigeration respectively. The ammonia produced as liquid is about 99% (wt) and stored in hortonsphere for sending to urea plant for urea production. The conversion of H2 to NH3 in synthesis loopis about 14–16% (Vol) and inert gases from synthesis loop is sent to ammonia recovery section. Onlymake up synthesis gas (H2 + N2) is fed to the NH3 reactor using KM1 and KM2 catalyst, to the extentammonia is produced due to catalytic conversion of H2 and N2 into NH3.

3H2 + N2 = 2NH3 ∆H = –22400 Btu/1b mole

The overall energy required per ton of ammonia various from 5–10 Geiga calories/ton dependingon patented process of Haldor Topsoe, Texaco, Kellog, etc.

(ii ) In case of LSHS, desulphurisation by cold methanol is carried out after raw gas generationin gasifier using oxygen from air separation unit and O2 compressed to 28 Kg/sq.cm. In the gasifierpartial oxidation reaction takes place in the flame with generation of raw gas (H2 + CO).

When refinery naphtha (boiling range 170°C) is used as raw material, two stage desulphurisationis carried out first prior to gasification in a reactor. The rest of the process like CO conversion, CO2absorption using hot Pot. Carbonate soln. with V2O5/As2O3 as corrosion inhibitor, (As2O3) is normallynot used now due to pollution) and methanation followed by high pressure ammonia synthesis. Byproduct carbon pellets is obtained when LSHS is used for gasification.

Fuel used in reforming section is same as starting raw material viz N.G. or naptha (Vaporised).Texaco, USA is the licensor for gasification section. Other process licensors are ICI, KELLOG etc.

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4 REFERENCE BOOK ON CHEMICAL ENGINEERING

4. DETAIL PROCESS DESCRIPTION FOR AMMONIA PRODUCTION USING N.G. AS FEED STOCK

Natural gas is compressed to 41 ata and preheated to 400°C in N.G. fired heaters and sent fordesulphurisation using comox catalyst (Cobalt – moly and Zinc oxide) catalyst. The type of catalystrequired depends on inlet sulphur concentration as H2S and organic sulphur. The gas is then mixedwith H.P. steam at 40 ata and 370°C. The mixed N.G. is then (further) heated in mixed gas heaterupto 500°C and fed to primary reformer at 32 Kg/Cm2g containing primary reformer catalyst innickel tubes of HK-40 material. For 600 MT per day ammonia plant 240 nos. tubes of 6" diameterin vertical row are required. The primary reformer furnace is generally having side fired N.G. burnerswhere N. G. is burnt as fuel (top and side fired burners are also used in primary reformer). Thereformer furnace temp. is kept at 1000°C and steam carbon ratio is maintained in the primaryreformer tubes between 3–4. The tubes expand upwards and gas flows from top to bottom. Primaryreformation of N.G. takes place inside the tubes at 700–800°C in presence of nickel based catalyst.The tube life is around 100,000 hours.

The exit gases from P.R. at 30 Kg/sq.cm and 795°C is further reformed in secondary reformerat 950°C. In the secondary reformer in the presence of catalyst, further reformation takes place at31 ata when some H2 burns to produce heat necessary to convert most remaining feed stock to H2,CO and CO2. Air is fed to S.R so as to provide necessary N2 in synthesis gas in the molar ratioof 1:3 (N2 : H2). The exit heat from S.R gases is recovered in super heaters, N.G. heaters and airheater and mix gas heater in the reformation section. The hot S.R exit gas, containing 12% CO at1000°C, is then sent to R.G boiler to generate H.P. steam followed by two stage catalytic COconversion when equivalent H2 is produced from CO in raw synthesis gas, (H2 + CO).

CO + H2O CO2 + H2

General Reaction in Primary ReformerCnH2n+2 + nH2O → nCo + (2n + 1)H2 General reaction

CH4 + H2O → CO + 3H2 1

CH4 + 2H2O → CO2 + 4H2 2

C2H6 + 4H2O → 2CO2 + 7H2 3

C3H8 + 6H2O → 3CO2 + 10H2 4

C4H10 + 8H2O → 4CO2 + 13H2 5

C5H12 + 10H2O → 5CO2 + 16H2 6

C2H6 + 2H2O → 2CO + 5H2 7

C3H8 + 2H2O → 2CO + 7H2 8

C4H8 + 2H2O → 4CO + 8H2 9

C5H10 + 5H2O → 5CO + 10H2 10

Reactions 1 to 6 are major reactions. Other reactions possible in varying conditions of pressureand temp. in the primary reformer are:

COS + H2O → CO2 + H2S

2CO → C + CO2

C + H2O → CO + H2

Page 16: Reference Book on Chemical Engineering v. 1

FERTILISERS 5

CO2 + C → 2CO

CH4 + CO2 → 2CO + 2H2

2CH4 → C2H6 + H2

H.T. CO conversion is carried out at 327°C/427°C when CO at exit is around 2–3% and LTCO conversion at 210°C/330°C. The CO and CO2 content of L.T. converter is 0.30% and 18.5%respectively. The heat in exit gases from H.T. converter is used to preheat boiler feed water heatersand L.T. converter outlet is used to produce, L.P. steam. The L.T. exit gas is then sent to decarbonationtower to remove CO2 with either Vetrocoke soln. or Benfield soln. (Pot. Carbonate with V2O5). Boththe CO2 removal processes are proprietory items. Now a days Vetrocoke soln. (hot potash withAs2O3) in not used due to pollution problems. Corrosion in-hibitors As2O3/V2O5 forms a stablepassive oxide film in towers which prevents corrosion; absorption of CO2 by Pot. Carbonate soln.takes place as per the following reaction :

K2CO3 + H2O + CO2 → 2KHCO3

Regeneration of the bicarbonate is done by heating of the soln. in the desorption tower withreboiler :

2KHCO3 → K2CO3 + CO2 + H2O

Heat supply to reboiler is by steam. The generated CO2 gas from desorption tower/regeneratortop is cooled in a cooler to remove condensate and sent to urea plant.

The decarbonated gas at 60°C and 26 ata pressure is preheated by hot methanator outlet gasand partial H.T. CO converter gas upto 315°C and feed to methanator where remaining CO and CO2are converter catalytically by iron oxide catalyst to methane.

2CO + 5H2O → 2CH3 + 2H2O

The heat recovery as well as operating parameters in reformation section to methanator variesaccording to process licensor scheme. Methanator is often deleted and in its place liquid N2 washis carried out in process licensor e.g., C.F. Brown Process.

The hot gas from methanator after heat exchange, cooling and condensate separation is thesynthesis gas having H2, N2 ratio within 3 (molar) and CO + CO2 within 5ppm, CH4 = 0.75%. Thesynthesis gas is sent to compressor at 45°C and 25 ata pressure for compression to 200–250 Kg/sq. cm. The total pressure drop to primary reformer to methanator is designed at 5–6 Kg/cm2.

In the synthesis loop, make up pure synthesis gas mixture along with recirculated synthesis gasis compressed and cooled in cold exchanger (Tube side) and in the ammonia cooled condenser andammonia separated in secondary cold ammonia separator. The gas then enters shell side of coldexchanger and then shell side of hot exchanger and then to ammonia converter packed with KM1(often KM2 also) iron catalyst where NH3 is formed at a temp. of 425°C–500°C. Reactor temp. iscontrolled by by-pass gas valve in each of 3 catalyst beds.

H.P. steam is generated in boiler coil inside the NH3 reactor. The converted exit gas is thencooled in primary water cooled condenser from 70°C to 38°C and then to sec. ammonia cooledcondenser. The liquid ammonia condensed is separated in primary separator, sec. separator andunconverted gas is recycled to the recirculator and a small part is purged to ammonia recovery sec.from recycled gas to keep inerts, Argon, CH3 within limit. Liquid ammonia from primary and twosecondary separators is put in let down tank from where it is taken to Horton sphere for storage.

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6 REFERENCE BOOK ON CHEMICAL ENGINEERING

H.P.

Auxiliaryboiler

To P

lant

ne

twor

k

P rimary reformation

M .P. S erviceboile r

S team networkAir se con daryreform a tion

H.T. CO.-conversion

L.P. boiler for steamgeneration

L.T.C O-conversion

CO absorption2

CO desorption2

Methanation

Amm onia synthesisand refrigeration sec.

Amm onia storage

Lig am monia toconsuming plants

CO

to u

rea

2

Fig. 1. N.G. steam reformation (HTAS) for ammonia synthesis in (HTAS) process.

The flow scheme of gases in the synthesis section also varies as per process licensor’s designdepending on the extent of waste heat recovery from syn. converter. Often two syn. converters arerequired for greater conversion to ammonia as in C.F. Braun’s Process as well as some design ofUhde. CO2 absorption also varies – pressure swing absorption (ICI) and regeneration by flashing andphysical absorption using selexol/sepesol and MDEA Process (BSAF) and more common Process ofCO2 removal by DEA and MEA depending on process adopted by process licensor.

Page 18: Reference Book on Chemical Engineering v. 1

FERTILISERS 7

5. SYN. GAS (CO + H2) GENERATION BY NONCATALYTIC FUELOIL/LSHS GASIFICATION

There are two process licensors Texaco and Shell for production of raw syn. gas by non-catalytic gasification of Fuel Oil/LSHS using oxygen by the partial oxidation route. Texaco had,however, developed a gasification process using these feeds stocks with enriched air (with oxygen).

General Formula

CmHnSr + mO2 → m/2 CO + (n/2 – r) H2 + rH2S.

Side ReactionCmHnSr + (r – n/2 + 2) H2 → CH4 + (m – 1) C + rH2S.

H2O + C → H2 + CO

H2O + CH4 → 3H2 + CO

H2O + CO → H2 + CO2

Partial Oxidation of Heavy Fuel Oil (feed stock)C15H24S2 + 15/2 O2 → 15CO + (24/2 – 2) H2 + 2H2S

or C15H24S2 + 7.5 O2→ 15CO + 10H2 + 2H2S

In Case of Full OxidationC15H24S2 + 20O2

→ 15CO2 + 10H2O + 2H2S

Side ReactionsC15H24S2 + (2 – 24/2 + 2) H2 → CH4 + (15 – 1) C + 2H2S

or C15H24S2 + 8 H2→ CH4 + 14C + 2H2S

H2O + C → H2 + CO

CH4 + H2O → 3H2 + CO

CO + H2O → H2 + CO2

ProcessOxygen gas from Air Separation Plant is compressed to 52 Ata, mixed with H.P. steam and

the mixed gas is led into partial oxidation gun along with preheated heavy fuel oil inside the gasificationreactor where flame reaction takes place producing raw syn. gas (H2 + CO). The nitrogen in fueloil is converted to molecular N2 and sulphur to H2S and small amount of COS. The gases are thenquenched with water to remove unreacted fuel oil. The carbon water from quench vessel in thensent to carbon recovery section where carbon is separated and pelletised for use in service boilerand water slurry recirculated with the make up water to quench vessel. The H2S in raw syn. gasat 51 ata and 48°C is then sent to rectisol section for desulphurisation with cold methanol at –20°C.Due to presence of considerable sulphur compound (H2S, COS) etc. cold methanol is used in thisprocess (Rectisol) using ammonia refrigeration. Sulphur is reduced to 0.1 ppm.

The gases are then led into HT CO conversion after heating where shift reaction takes placeat 327/420°C and most of CO is converted to H2.

CO + H2O → CO2 + H2

The exist gases from HT CO converter contain 0.3% CO and CO2 gases are absorbed withcold methanol at (–50°C) in Rectisol section where most of CO2 is physically absorbed in cold

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8 REFERENCE BOOK ON CHEMICAL ENGINEERING

methanol which is then regenerated by heat and flashing. The generated CO2, about 96%, is sent toUrea Plant and other consuming plant. The regenerated methanol soln. is sent to CO2 absorber. Theexit gases from absorber still contain some CO and CO2 along with Methane and Argon. The gasesare then first adsorbed in molecular sieve vessel where CO2 is adsorbed (below 10 ppm) and methanebelow 50 ppm. The purified gases are then sent to liquid Nitrogen wash tower where CO, CH4 andArgon are removed and after regeneration of liquid Nitrogen containing CO, CH4 are Flashed out andstored for use as a fuel. The purified mixture of Hydrogen gas and Nitrogen, in the ratio of 3 : 1,is then compressed to 200 – 250 Kg/cm2 along with recycle gas containing unreacted Hydrogen,Nitrogen and some Ammonia is sent to syn. reactor where after preheating enters the catalysts bedsin ammonia converter where ammonia is produced at 500°C.

3H2 + N2 = 2NH3 ∆H = –22400 BTU/1b mole

H.P. Steam is produced in the syn. reactor, flashed in syn. boiler and used in the process.

Serv ice boiler

Ste

amne

twor

k

Carbon pellets

Desulphurisationby cold methanol

H.T. CO conversion

Liq. N2 wash

LSHS (Storage)

Shell gasification

CO absorptionby rectisol process

2

CO 2 desorption

Ammonia synthesisand refrigeration sec.

Lig. ammonia storage

Lig. ammonia toconsuming plants

Air separation

Tail gas

L iq .N 2

A ir

CO

to u

rea

2

O2

Fig. 2. Shell gasification (partial oxdn.) ammonia synthesis process.

Page 20: Reference Book on Chemical Engineering v. 1

FERTILISERS 9

Table 1

CO2 Removal Process

Plant Supplier Uhde activated MDEA of Uhde low heat hot potashBASF U O P

H.P. Boiler FW preheating 31.2% 29.2%

L.P. steam generation 14.9% –

Heat for CO2 removal 31.4% 49.9%

Demineralised → water 22.5% 20.9%preheating

Total heat available 100%

Table 2

CO2 Removal Process

Process MDEA (BASF) Low heat hotpotash (UOP)

Absorber outlet CO2 100 ppm 1000 ppm

Kcal/NM3 368 777

CO2 recovered in 96.51 99.52regenerator, %

CO2 purity (dry), % 99.75 99.06

Table 3

UHDE Ammonia Synthesis Loop Data

H2/N2 ratio 2.95

No. of syn. reactor OneMu. syn. gas 27 bar, 6°C

Ammonia separation temperature –10°C

125 bar steam generation t/t NH3 1.17

Waste heat used in H.P. steam 60%raising%

Waste heat removal in cooling water 14.81%

Chiller duty 25.01%

Total heat available 100%

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10 REFERENCE BOOK ON CHEMICAL ENGINEERING

Table 4

Energy Consumption for Ammonia Plant (N.G. based)

Process Reformation and syn. –HTAS, HTASCO2 shift (Two stage PDIL) and

Methanator (PDIL)

Plant capacity 600 MT/day 1000 MT/day

Location India Europe

N.G. (feed stock Fuel*) 8.49 7.641 Gcal/Te

G.cal/Te

N.G. Methane content 78–91% (Vol) Over 90% (Vol)

N.G. per ton ammonia 1218 SM3 N.A.

Electrical Power (excl. CT) 61.20 KWH/Te 28.6 KWH/Te

Polished water 4.302 M3/Te 4.31 M3/Te

CO2 Production rate 1.132 Te/Te N.A.

Cooling water 643 M3/Te 210 M3 (sea water)/Te

M.U. water for C.T. 13.8 M3/Te N.A.

CO2 removal process Benfield N.A.

Energy per ton ammonia, 10.875 7.02G.cal/Te

*Correspond to full enthalpy of steam and water at 0°C.

6. DEVELOPMENT IN AMMONIA PRODUCTION

(1) Raw Syn Gas GenerationMost of the fertilizer plants in the world use steam methane reforming process followed by

partial oxidation of heavy fuel oil (LSHS) as feed stock. One smaller plant uses coal gasification toproduce raw gas. MW Kellog of U.S.A. had developed reforming exchanger system for raw syn.gas generation. The reforming exchanger contains open tube catalyst tubes hanging from exchangertop. Oxygen mixed with air, steam and NG feed (2/3rd) are 1st fed to catalytic adiabatic reformerwhere certain amount of reforming takes place at a temp. of 954–1010°C. Nearly 1/3rd of balanceprocess feed NG and steam enter the reforming exchanger from top while adiabatic reformer effluentalso enters the shell side of reforming exchanger providing recovery of heat for reforming reaction.The outlet gases from reforming exchanger goes to feed/effluent H.E. where mixed gases arepreheated and reformed gases then follow the heat recovery system of CO shift converters, CO2removal and methanation and compressed prior to entering ammonia synthesis loop.

Table 5

Process Data for Reforming Exchanger (Kellog)

O2 in enriched air Upto 30%

Mixed feed pre heat temp. 480° – 620°C

Overall, steam/carbon ratio 3.3 – 3.8

Adiabatic reformer exit temp. 925° – 1040°C

Design methane slip 0.5 – 0.7% (vol) dry

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FERTILISERS 11

However, the reforming exchanger system, where no secondary reformer is used, changes theconventional heat balance system of the process. Most of the high temp. heat, via the heat exchangerreformer is returned to the process and will thus not be available for H.P. steam production andexcess of low temp. heat will be available for med. or L.P. steam production which can not be utilizedin ammonia plant and H.P. steam must be generated in auxiliary boiler or service boiler for use inH.P. steam turbine drive of syn. gas compressor. The overall energy efficiency will entirely dependupon the efficiency of auxiliary steam generation.

(2) CO2 Removal ProcessThere are several proprietory processes viz Vetrokoke hot potash system using arsenic oxide,

Benfield process using V2O5, Catacarb process, MDEA process of BSAF, Hot Potash process ofUOP, low temp. (–50°C) Rectisol process. In addition, MEA and DEA of CO2 process is also used.In all these processes, absorbed CO2 rich soln. from packed absorber is regenerated by heating andflashing to low pressure (0.15 Bar). The efficiency depends on heat economy for regeneration ofsoln. as well as power recovery by soln. turbine in the absorber outlet soln. to recover part of powerreqd. for pumping the regenerated soln. to absorber. About 40% recovery is possible. Heat requiredfor regeneration of soln. varies from 370–800 Kcal/NM3 CO2. CO2 conc. from 96–99% (vol) isrecovered CO2.

(3) CO Shift ConversionGenerally two stage (HT and LT) shift reactor is used with L.P. steam (3.5 ata) generation at

outlet of HT converter. The temp. at HT converter is maintained at 330°–425°C and that of L.T.converter, 210°–330°C.

Shift reaction : CO + H2O → CO2 + H2

(4) MethanationThe remaining CO (0.3%) and CO2 in raw syn. gas after CO2 removal is removed in catalytic

methanator working at 315°/220°C.

Methanation reaction: 2CO + 5H2 → 2CH3 + 2H2O

CO2 + 3½H2 → CH3 + 2H2O

Instead of methanation often cryogenic separation is used to remove residual CO, CO2 Methaneand Argon and molecular sieve is used for adsorption of CO2 for plants having air separation unitfor oxygen requirement in partial oxidation process.

(5) Ammonia Synthesis

The pure syn. gas with H2/N2 ratio of 2.95 CO and CO2 maxm. 5 to 10 ppm each iscompressed in syn. gas compressor to 200–250 Kg/sq. cm pressure and sent to syn. loop forconversion to ammonia in catalytic ammonia converter having 3 beds of KMI and KMII catalyst. Theconversion to ammonia is 15–20% and considerable heat is produced which is utilized to generateH.P. steam. The reactor effluent after heat recovery for H.P. steam generation is cooled first by watercooling and separation of ammonia followed by 1–2 steps ammonia cooling when remaining ammoniais separated. The vapour refrigerent ammonia is sent to ammonia compressor where ammonia iscompressed, liquefied and sent to synthesis section. The unconverted syn. gas is recycled to reactorvia recirculator where it is pre-heated for further conversion along with make up gas. H.P. steamgeneration, as per modern trend, is to generate H.P. steam at 110–125 ata.

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12 REFERENCE BOOK ON CHEMICAL ENGINEERING

Steam Net Work

A stable steam net work is key to operating stability in ammonia plant; normally H.P. steam isused in syn. gas compressor turbine and part of it is extracted at 38–40 ata for process aircompressor and refrigeration compressor drives. L.P. steam from CO conversion is used in condensatestripping and regenerator heat duty in CO2 recovery section.

Plant Capacity

Modern ammonia plant is constructed as large tonnage plant with capacities ranging from min.600 Te/day to 1000–3000 Te/day and is mainly based on N.G. or naphtha or LSHS as feed stock.The price of N.G./LSHS/Napfha per million Kcal/BTU is a key factor in economics of ammonia plantand fixes the criteria of plant design basis and economics, of payout time, I.R.R, R.O.I. etc. In Fig.1 and Fig. 2 block diagrams for ammonia synthesis process based on N.G. and LSHS is given.

7. UREA PLANT

Now a days most urea plants are designed, based on Stamicarbon’s CO2 stripping process orSnadom’s ammonia stripping process. Toyo Engg. Corpn’s total soln. recycle, ACES process is usedin many plants and also Technimont’s IDR process which uses both CO2 and ammonia strippingfinds its use in some plants.

Process : Conventional Total Soln. Recycle

Preheated liquid ammonia and CO2 gases under 190–200 Kg/cm2 press are reacted in anadiabatic reactor at 180–190°C in presence of recycled unconverted carbamate soln. The reactor feedratio of NH3 : CO2 : H2O is 3.5–4 : 1 : 0.5 to 0.6.

Reaction : 2NH3 + CO2 → NH4 COONH2 ∆H = –38 Kcal/Kgmole

NH4COONH2 = NH2CONH2 + H2O ∆H = 5 Kcal/KgmoleUrea

Overall reaction :

2NH3 + CO2 = NH2CONH2 + H2O ∆H = –33 Kcal/Kgmol

A CO2 conversion efficiency of 60–70% is achieved in the reactor and the unconvertedammonium carbamate decomposed in 2/3 stages. The decomposed gases (NH3, CO2 and H2O) areabsorbed in corresponding absorbers with rectification for separation of excess ammonia at 2nd stage(16–17) Kg/cm2; recycle soln. from 3rd stage absorber is successibly sent to next higher stages andfinally pumped from 1st stage condensor to reactor by H.P. carbamate recycle pump. Excessammonia vapour recovered from 2nd stage absorber rectification stage at top is condensed andrecycled back to reactor by H.P. NH3 feed pump along with makeup NH3 duly preheated. Make upCO2 gas is compressed in centrifugal/reciprocating compressor and fed to reactor. The 70–75%dilute urea solution from 3rd stage distiller is concentrated in two stage vacuum concentration to98.5–99% urea melt and prilled in a I.D. prilling tower having rotating (370–380 rpm) bucket sprayer(1–1.3 mm hole). The specific load in a prilling tower is 0.17– 0.19 tonnes/m2 and air rate = 1000NM3/te with air velocity of about 0.47 m/sec.

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FERTILISERS 13

Stamicarbon CO 2 Stripping Process

1st developed by Stamicarbon NV in 1965. It is based on Henry’s law.

The equation which governs the principle of stripping gases, CO2/ammonia in decompositionof unconverted carbamate, is given below:

2NH3 + CO2 NH4OCONH2 ∆H = –38 Kcal/Kgmol.

Eqn. C K C Ccarb. eq. NH CO32

2=

where Keq. is the equilibrium constant for the above reaction and Ccarb CNH32 CCO2 are the concentrations

of carbamate, NH3 and CO2 respectively.

If CO2 gas is passed through the solution containing unconverted carbamate, the above reactionbecomes

Ccarb = Keq × O2 × 2COC (due to high CO2 conc. ion, NH3 concentrate becomes 0 or negligible)

= 0

Therefore, carbamate conc. will be 0 or nearly so when CO2 is used as a stripping gas. Theoperating pressure in the syn. loop consisting of reactor, stripper and carbamate condensers is 150atm and NH3 : CO2 ratio in reactor is 2.8 and conversion of CO2 to urea is around 58–60%. TheNH3 : CO2 ratio is the syn. loop is 2 which ensures smaller NH3 feed pump. The overall CO2conversion efficiency is 80–85%. The stripper is having vertical titanium tubes through which reactoreffluent descends in a thin film and the tubes are heated outside with steam at 160–180°C. All CO2gases at 150 Kg/cm2 are passed upwards through the tubes from bottom and the stripped reactoreffluent is devoid of 90% CO2 and NH3 and hence carbamate. The stripped NH3 and CO2 gases alongwith water vapour are led into carbamate condenser which is also fed with an amount of ammoniathrough an ejector which draws reactor effluent equivalent to the amount of CO2 introduced into thestripper bottom. The ejector effluent containing make up ammonia and reactor effluent flows to thefalling film type carbamate condenser where condensation takes place and the heat evolved is usedfor waste heat steam generation at low pressure. The outlet stream from HP condenser containingrecycle carbamate solution together with NH3 and CO2 gases, flows into the reactor. The stripperexit solution after pressure reduction, is led to rectifying column at low pressure where urea solutionis removed of residual carbamate and dilute urea sol. 72–75% is led into two stage vacuum concentratorsat prilling top and 99% urea melt from 2nd stage concentrator is prilled using spinning bucketssprayer in prilling tower with induced airflow. There is only one recycle stage after HP syn. loop.

Since the process works on low excess ammonia, corrosion in HP syn. loop is prevented byintroducing 2–3% oxygen along with make up CO2 gas. The better corrosion resistant material(Titanium tubes) in stripper and condensor is used; inert gases are removed from reactor top in inertwashing tower and condensed NH3 and CO2 is recycled to H.P. condenser.

Condenser. The vapours from rectifying column are condensed in a condenser and remainingNH3 and CO2 along with inerts are washed in inert washing column with condensate from vacuumsection. A part of condensate from vacuum section is hydrolysed in a urea hydrolyser and ammoniaand carbon dioxide vapours are recovered.

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14 REFERENCE BOOK ON CHEMICAL ENGINEERING

The reactor volume is slightly bigger and vapour pocket exits at top. The reactor is providedwith sieve trays for better vapour liquid mixing and to prevent back flow. Stamicarbon CO2 strippingprocess is being used in a large number of urea plants in the world. The plant is economical as capitalcost and variable cost are lower.

Snam Progetti NH 3 Stripping Process

The principle of the process is given by the following equations :

(A) NH2COONH4 →← CO(NH2)2 + H2O

ammon. carbamate urea

(B) 2NH3 + CO2 →← NH2COONH4

Ammon. carbamate

(C) 2

3 2

0.53 PsP =

3 [NH ] .[CO ]

where P = dissociation Pressure of liquid carbamate.

In this process pressure in the syn. loop using ammonia as stripping agent of reactor, NH3stripper (titanium tubes) and H.P. carbamate condenser, is maintained at 150 atm; NH3 : CO2 in thereactor is 3 : 8 and temperature 185°C with conversion efficiency of 65–67%. Due to high NH3 :CO2 ratio, there is high residual NH3 content in the stripped solution leaving the stripper. The overallCO2 conversion efficiency in the syn. loop is 85%. Two carbamate decomposition and recoverystages, down stream of syn. loop, and a separate NH3 recovery unit as pure component have beenprovided.

Two H.P. condensers have been provided with steam recovery at 4.5 atm and 6 atm respectively.All CO2 with 0.3% oxygen for condensers passivation-with little by pass to stripper (as more heatis produced than required to maintain reactor temp.) to which reactor effluent from top enters. Thereactor effluent passes through the stripper against an ascending stream of NH3 vapour from NH3evaporation section. Steam at 25 atm is passed in the shell side of stripper operating at 170–180°C.The stripper effluent contains only 2% carbamate and followed by two stages of decomposition andrecovery at 17 and 3.5 atm and the 75% urea solution obtained is concentrated in 2 stage vacuumconcentrator to get 99.5% urea melt which is sprayed from a rotating bucket (300 rpm) in aninduced draft prilling tower and prills at 50°C is obtained from bottom. Free fall of urea melt inP/T is 30 m and overall ht. of P.T with vacuum concentrators and dedusting system at top of P.Tis about 44 m.

The stripped NH3, CO2 and H2O gases are condensed in 1st H.P. condenser with steam raisingat 6 atm, and outlet condensed carbamate, along with uncondensed vapour, is fed into 2nd H.P.condenser where full condensation of gases occur and then recycled to recover via H.P. ejectoroperated by H.P. ammonia feed from ammonia pump. The 1st stage recycle solution from H.P.absorber is pumped to no. 1 H.P. condenser and L.P. condenser weak solution is pumped to H.P.condenser. NH3 and CO2 is absorbed from vacuum condensate and recycled back to L.P. condenser.Fig. 3.

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FERTILISERS 15

L R C

P R C

L R C

SteamCond.

NH 3

Urea solution (Two stagedecom positionrecovery section)

Inert Vent

Ejector

NH3

L.P.Steam

W Hboiler

Reactor

CarbamateCondenser

Snam Progetti UreaSynthesis-loop

Stripper

Fig. 3

8. TEC’S ACES (ADVANCED COST AND ENERGY SAVING) PROCESSThe process uses an isobaric syn. loop consisting of reactor with two strippers at 185/187°C

and H.P. carbamate condenser working at 175 atm pressure. The reactor temp. is 190°C and NH3CO2 feed ratio is 4.0 and CO2 conversion efficiency is 68%. Most of CO2, after compression in acentrifugal compressor, is passed through stripper, having sieve plates at top, and tube bundlethrough which reactor effluent falls as a failing film layer. In the effluent, NH3 and CO2 content is12 and 14% respectively. The tube bundle is heated by medium pressure steam (25 atm). Most ofthe unconverted carbamate is decomposed at high partial pressure of CO2 and the gases moveupwards through sieve plates thus reducing moisture in NH3, CO2 gases which move into 1st H.P.condensor where it is condensed in presence of carbamate soln. from H.P. scrubber where reactoroutlet gases are washed with recycle carbamate from H.P. scrubber. The steam at 5 atm is raisedin 1st decomposer. A part of stripper outlet gases is also sent to 2nd H.P. decomposer to the extentheat is required to heat up the stripper outlet solution to decompose residual carbamate.

The urea solution with low carbamate content from shell side of 2nd H.P. decomposer is sentto H.P. decomposer where it is heated by steam in shell side. The solution outlet of H.P. decomposeris then sent to LP decomposer with CO2 stripping introduced at bottom. It is a packed tower withbubble cap plates at top. The gases from L.P. decomposer top is condensed in shell and tube L.P.absorber and absorbed solution is recycle back to H.P. absorber. The carbamate solution from H.P.absorber is recycled to 2nd H.P. condenser and H.P. scrubber.

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16 REFERENCE BOOK ON CHEMICAL ENGINEERING

The off gases, with inert from air injection in H.P. scrubber are further absorbed in inertwashing column after pressure reduction. The dilute urea solution from L.P. decomposer is sent totwo stage vacuum concentrators and 99.5% urea melt is sprayed into prilling tower top. The ureaprills at the bottom of the tower is cooled in a fluidized bed cooling system. The vacuum condensatefrom vacuum section is stripped in plate tower and stripped gases are sent to L.P. decomposer. NoNH3 recovery as pure component is considered and all NH3 is fed to reactor.

9. MONTEDISION’S IDR (ISOBARIC DOUBLE RECYCLE) PROCESSHere reactor, NH3 stripper, CO2 stripper both working at 200°C and H.P. carbamate condenser

and a post condensor operate at 200 atm pressure. The CO2 conversion efficiency in reactor is 70%and corresponding NH3 : CO2 feed ratio is 4.25 with water: CO2 ratio 0.55. The reactor is dividedinto two section by a partition plate. The reactants are fed to the bottom of upper section, raisedto top and through down comes to the bottom of lower section and flows upwards to outlet to the1st H.P. CO2 stripper. The NH3, CO2 stripped vapour flows to reactor upper section where theseare condensed and keep reactor temp. at 185–190°C.

The stoichiometric NH3 feed is arranged at different temperature levels to reactor upper section,to 1st H.P. decomposer and to reactor lower section. The last stream is meant to establish the zonedesign ratio of NH3/CO2 not yet converted.

In the last H.P. NH3 stripper, most of residual carbamate is decomposed and recycled to thereactor in vapour phase. The heat required is supplied by M.P. stream. The solution from the stripperis conveyed to the 2nd H.P. stripper where whole of make up CO2 is fed as stripping agent. Bysupplying heat (M.P. steam), the 2nd stripper outlet contain 40% CO2 and 14% ammonia is sent tothe M.P. stage purification section, working at 23 atm after pressure reduction where it is heated byrecovery steam at 157°C. The vapours from 2nd H.P. stripper are sent to H.P. condenser togetherwith most recycle carbamate solution from M.P. carbamate condenser. Steam is generated in M.P.carbamate condenser at 7 bar. The carbamate solution from H.P. carbamate condenser flows bygravity into the reactor. The non condensable gases from H.P. carbamate condenser are cooled andpartially condensed in a post carbamate condenser which also flows by gravity into the reactor andunabsorbed gases from post carbamate condenser is sent to inert washing column after pressurereduction. Waste heat from post carbamate condenser is used to generate 3.5 atm steam. The vapourfrom M.P. condenser is sent to concentrator for heating and concentration of urea solution from L.P.decomposer and carbamate solution at 120°C is recycled to H.P. carbamate condenser and postcarbamate condenser. L.P. decomposer is heated by 7 atm steam at 146°C. Urea solution from L.P.decomposer is concentrated to 99.5% concentration in 2 stage vacuum concentrators usually at thetop of prilling tower to reduce biuret and prilled in a rotary spinning bucket (holes–1.3 mm). Air isused along with make up CO2 gas (0.2% oxygen) as well as a small injection of air +H2O2 in H.P.stripper is made to passivate stainless steel to prevent corrosion.

10. STORAGE FOR FERTILISERSilo volume to surface area ratio is kept smaller. Usually RCC parabolic silo is constructed with

air conditioning plant to keep R.H. less than humidity of stored fertilizer. Usually critical humidity,around 65–70% in silo, is to be maintained to prevent moisture absorbtion to prevent caking.Air conditioning is required when R.H. is higher than 70–80%. Bagging is usually done in baggingplant.

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FERTILISERS 17

Table 6

Specific Consumption of Raw Materials and Utilities in Large Tonnage Urea Plant.

Process NH3 t/te CO2 t/te Steam Export Process Ele- Cooling watert/te Steam t/te ctricity kwh/te m3/te

Stamicarbon 0.57 0.75 0.775 – 15 62.5

CO2 stripping 25 bar ∆t = 10°C

Snam 0.57 0.74 0.83 – 20 70

Projetti NH3 23 bar ∆t = 10°C

Stripping

TEC-ACES 0.57 0.75 0.70 0.09 30 60

Process 100 bar 6 bar ∆t = 10°C

Montedison 0.568 0.736 0.71 – 18 75

IDR process 105 bar ∆t = 10°C

Table 7

CO2 By Product Gas from Ammonia Plant

Constituents Values

CO2 98.5%, saturated at 45°C and 500 mm W.G. Pressure

CO 0.60

H2 0.65

N2 + Ar 0.1

Sulphur < 0.5 ppm

Table 8

N.G. Analysis

Constituents Values

CH4 78–91%

C2H6 6–10

C3H8 5–6

ISO Butane (C4H10) 1–1.5

N Butane 1.3–1.4

ISO Pentane (C5H12) 0.3–0.4

N Pentane 0.14–0.25

NCV 10377 Kcal/m3

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18 REFERENCE BOOK ON CHEMICAL ENGINEERING

Table 9

Comparative Statement on Energy Consumption

Kellog UHDE PDIL MHI-CHIYODA

1. Ammonia Plant

(i) Process route Kellog’s steam ICI steam PDIL/HTAS HTASreforming reforming

(ii ) CO2 removal Benfield MEA Benfield Catacarb

(iii) Synthesis Kellog UHDE Ammonia converter CCC(HTAS) rest PDIL

(iv) Rated plant 900 MTD 900 MTD 600 MTD 900 MTDcapacity

2. Feed Stock Fuel NG NG NG NGEnergy Mkcal/MTGuaranteed

(i) Feed + Fuel 10.0569 9.97 10.933 9.59

(ii ) Steam 0.0216 (-) 1.008 – 1.37import/export (export)

(iii) Elec. power 0.099 0.12557 0.2185* 0.05(excluding C.T.)

(iv) Total energy 10.1715 9.0875 11.1515 11.01(excluding C.T.)

3. Uure Plant Stami-carbon Stami-carbon PDIL Stami-carbonconventional

(i) Process route CO2 CO2 stripping 3 stage total CO2 strippingstripping solution recylce

with steam reco-very in 1st cycle

(ii ) Rated plant 1620 MTD 1550 MTD 1167 MTD 1600 MTDcapacity

4. Raw MaterialConsumption(Guaranteed)

(i) Liquid NH3 MT/ 0.58 0.58 0.590 0.592MT urea

(ii ) CO2 MT/MT 0.77 0.77 0.77 0.775urea

5. Energy,Mkcal/MT

(i) Feed ammonia 5.899 5.2707 6.5794 6.517

(ii ) Import steam 0.8205 0.7998 1.0376 1.0with pressure and (39 ata, (110 ata, (45 ata, 360°C) (66 ata, 43°C)temperature 380°C) 550°C)

Table Contd.

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FERTILISERS 19

(iii) Electric power 0.0215 0.0258 0.3586 0.03excluding (CT)

(iv) Export steam Used in Used in Used in 3.5 ata Used in silo(4 ata. satd.) deaeration in desulphurisa- network in urea dehumidification

ammonia tion for NG plant – 4.2 Te/hr 10 Te/hrplant, 10 Te/hr preheating,

16.2 Te/hr

(v) Total energy 6.741 6.0963 7.9756 6.7072(excluding C.T.)

6. Net Process 812 722 792 692Heat, Kcal/kgUrea

7. C.W., m3/MT 106 80 198 100

8. Turn Down 70% 70% 65% 70%Ratio

9. Energy for 0.9827 0.8635 1.5 0.9068Off-siteFacilities mkcal/mt Urea

10. Ovarall 7.7237 6.9598 8.438 7.614Energy forthe Complex,Mkcal/mt Urea

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20 REFERENCE BOOK ON CHEMICAL ENGINEERING

Fig. 4

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FERTILISERS 21

Fig. 5

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22 REFERENCE BOOK ON CHEMICAL ENGINEERING

Fig. 6

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FERTILISERS 23

Fig. 7

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24 REFERENCE BOOK ON CHEMICAL ENGINEERING

Fig. 8

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25

2Chapter

HEAT TRANSFER

1. INTRODUCTIONHeat is transmitted in the direction of the temperature drop by convection (contact), radiation

and conduction. In many cases all these types of heat transmission takes place simultaneously. Inshell and tube heat exchangers and other types of exchangers, the predominate phenomenon istransmission of heat by contact convection. In furnace and air heaters where gases are burnt to heata gas or other surface, both radiation and convection are to be considered. Heat conduction is theflow of heat with a material (solid, liquid or gas). In most cases a wall is concerned and the heatis flowing through it from one face to the other face as in a pipe through which a hot fluid is flowing.

Heat transfer considerations are of prime consideration in chemical process industry includingwaste heat recovery.

1.1 Convective Heat TransferIn convection (contact) mode of heat transfer is as per Fourier law, the quantity of heat

transferred is given by eqn.

Q = U.A. ∆tm where U = overall heat transfer co-eff, kcal/hr.m2.°C, where A = area of heattransfer, m2 based on O.D. of tubes, ∆tm = mean/logarithm temperature diff. in °C between heatemitting and heat absorbing media and Q = total quantity of heat transferred in the exchanger, kcal/hr.

However, overall heat transfer co-eff. is the sum of reciprocal of undivided film co-eff. is calledresistances to heat flow along the conduit (pipe) and resistance of metal wall plus fouling resistancesdue to foreign material depositing on both tube surfaces (inside and outside). For simplicity, for asingle layer wall (tube), the overall heat transfer co-eff. of heat transfer.

U = 1

1 fouling resistance1u

tu

+ + +λ

1

2

or1 2

1 1 1fouling resistances for

U inside and outside tubes

t

u u= + + +

λ

where, U = over-all heat transfer co-eff., Kcal/hr.m2°Cu1 = individual film co-eff. on the side of hot fluidu2 = individual film co-eff. on the side of cold fluid

t = wall thickness, m and λ = co-eff. of thermal conductivity forthe metal tube material, kcal/hr.m.°C.

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26 REFERENCE BOOK ON CHEMICAL ENGINEERING

The coefficient of heat transfer U depends on flow conditions, the type and temperature ofheating or cooling medium and configuration of areas of contact.

Temperature Difference (mean)The temperature difference between hot and cold fluids is the driving force of heat transfer in

a H.E. The flow of fluids (cold and hot) in the H.E. may be either countercurrent or parallel current;usually counter current flow is desirable as the quantity of heat exchanged remains constant. If ∆t1is the higher temperature difference and ∆t2 is the lower temperature difference at either end of H.E.

then arithmetic mean temperature 1 2

2

∆ + ∆t tis to be considered; if the ratio

1

2

∆∆

t

t is less than 2 or

2, while log mean temperature difference (LMTD) is to be considered if the ratio of 1

2

∆∆

t

t is more

than 2

∆tm = LMTD = 1 2

1

2

2.303 log

∆ − ∆∆∆

t tt

t

LMTD can be found from nomograph in Fig. 6 and ∆t1 and ∆t2 in Fig. 5.

1.2 Shell Side/Tube FluidIn H.E. generally the fluid which is more fouling is put in tube side due to ease of cleaning

and the other cooling or heating medium is put in shell side. A fluid having moderate to high pressand temperature is also passed through tube side to avoid high shell thickness of H.E.; viscous andcondensing fluids are passed through shell side.

1.3 Baffle Cut and Baffle SpacingFor making multipasses in shell side for better heat transfer in shell side fluid, 20–30% cut in

baffles are made for flow of fluid across tube bundle length. The extent of baffle cut and no. ofbaffles determine shell side fluid velocity as per design requirement. Increasing velocity in shell sidefor better heat transfer is by proper spacing of baffles. Baffles may be of annular or segmented cuttypes. The baffle spacing is usually equally spaced over the length between tube sheets ends. Bafflespacing is usually 1/5th of shell id.

1.4 Tube PitchTubes are laid in tube sheet for triangular pitch or square pitch or diamond pitch as per

requirement of shell diameter, tube spacing for heat transfer and fluid properties. The individual tubeends at both sides are sealed with tube sheet by tube expanders. In Fig. 3, layout of tubes fortriangular pitch is shown as well as formulae for square pattern layout are stated.

Mech. Design CodeHeat exchangers are generally designed as per TEMA class/ASME code/DIN standard.

Equations for determining heat transfer film co-effs.:-

Reynolds no =D ρ

µv

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HEAT TRANSFER 2 7

(i) For turbulent flow (Re no. > 4100 inside a clean tube; usually Dittus–Boltier equation is usedto determine surface or film co-effs.

u = 0.023

0.8D

D

λ ρ µ

v .

0.4C µ λ

p (for heating fluid)

or u = 0.023

0.8 0.3D C.D

v p λ ρ µ µ λ

(for fluid being cooled)

N.B. Cpµ

λ is Prandtl no., Dvρ

µ is Reynolds no. and Dµλ is Nusselt no., Nu and Re no. depend

on flow conditions and Prandtl no. indicated thermo-physico conditions of fluid.

(ii ) For gases in forced convection, perpendicular to banks of staggered tubes:

u = 0.13

0.7D

.D

v λ µ

(iii ) For condensing vapours in horizontal tube

u = ( )1/43 20.73 . .gλ ρ

And for vertical tubes u =

1/43 2. . .K0.94

L

g

t

λ ρ ′µ ∆

Where u = Surface or film co-efficient kcal/hr m2°C

λ = Thermal conductivity of fluid, kcal/m hr°C

v = Velocity, m/sec

D = Tube O.D. or I.D., m

µ = Absolute viscosity of fluid, kg/m.sec or Pa.S

Cp = Specific heat of fluid, kcal/kg°C

ρ = Density of fluid kg/m3

λ′ = Thermal conductivity of metal kcal/m.hr.°C

K = Latent heat of vapour, kcal/kg

L = Length of pipe, m

∆t = Temperature difference between vapour and metal, °C

g = Accln. due to gravity m/sec2

µ' = Viscosity of cold film kg/m.sec or Pa.S

1.5 Tube Wall Heat Flow Quantity

Q = 1 2

1 2

T T

/2.303 log

2 L

− π λ

r r

'

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28 REFERENCE BOOK ON CHEMICAL ENGINEERING

where Q = Heat Flow, kcal/hr

T1 and T2 = Temp. of inner wall and outer wall, °C

r1 and r2 = Raddii of inner and outer wall, m

L = Length of tube, m

λ′ = Thermal conductivity of metal wall, kcal/m.hr.°C

(i) For multipurpose heat exchangers having tube O.D., and tube I.D. diameter in meter theoverall heat transfer co-efficient is given by

U =

0 10

11

. 2.303 log2

+ + + ψ + ψλo o o o

i i i i

d d d d

u ' d d u dwhere,

uo and ui = outside and inside film co-efficient kcal/hr.m2.°C

do and di = outside and inside dia. of tube, m

λ′ = thermal conductivity of metal wall, kcal/m.hr.°C and

and ψo and ψi = fouling factors for outside and inside of tube

(ii ) In case of boilers and evaporator heating surface, overall co-efficient is given by

U = u1 + us

where,u1 = film co-eff. for hot water side

us = film co-eff. for tube metal wall

(iii ) For air heaters and super heaters u is given by:

u =1 2

1 2

.u u

u u+ kcal/hr.m2.°C

where u1 = film co-eff. for hot gas side of tube/coil

u2 = film co-eff. for cold gas side of tube/coil

Note : 1. Normally 60% more area is taken over calculated area due to uncertainties of mean data takenfor densities, sp. gravity, thermal conductivities, viscosity and sp. heat. Theoretically, R-S-S (root-sum-sq.)

system is considered, actual A (area) = 2( A)∑ ∆

1.6 Fouling FactorIn actual service, addln. resistance to flow of heat from hot side to cold side through metal

wall takes place resulting in reduction of respective film co-eff. with reduction of overall co-eff.Therefore, suitable fouling resistances (reciprocal of surface co-eff.) both hot and cold fluids arereqd. to be considered. Fouling resistances for different types of water are as follows:

2m hr°C

KcalDistilled water = 0.0005

Treated C.W. = 0.0005

Tube well water = 0.0003Sea-water = 0.004

Page 40: Reference Book on Chemical Engineering v. 1

HEAT TRANSFER 2 9

BFW = 0.001River water = 0.004Appln. Range:Temp. = 115–205°C rangeWater vel. = 3'/secWater temp. = + 52°C

2. TYPES OF HEAT TRANSFER EQUIPMENT2.1 Single or Multipurpose H.E

In multipurpose H.Es, pr. Drop of fluid through shell side increases as the fluid moves inrestricted space over baffle cuts but overall heat transfer co-eff. increase due to increased velocityof shell side fluid in the shell. Channel covers have reqd. compartments for directing tube side fluiddepending on no. of passes. Expansion it, if reqd. it is provided on shell.

2.2 Floating Head H.EsTo prevent unequal expansion of tube bundle resulting in tube leakage failure for fixed channel

covers, floating head tube bundle is provided with separate channel cover at floating head end.

2.3 Side/Top Fired Furnace for Indirect Heating of Gases/Water Inside Vertical Tubes

In reformation of hydrocarbon gases, side or top fired furnace heaters are used. In boilerfurnace with side fired burners are used for heating of water in tube along vertical wall. The tubesare connected to boiler drum. These furnaces are used in refinery, fertilizers and other plants.

2.4 Evaporators and Re-boilersThese are shell and tube H.Es and located either externally or internally with or without natural

or forced circulation. Steam is generally in shell side.

2.5 CondensersShell and tube H.Es for condensable vapours or steam is usually kept in shell side. Non-

condensable gases are purged from top of vessel or in case of steam, steam ejector is used. Incontact condensation, steam is condensed by water spray inside the empty condenser.

2.6 Regenerative H.EsIn a regenerative exchanger, where heat is alternatively stored and removed. The hot and cold

fluid passes through same route through the same exchanger. Two exchangers are required as onegets heated up by hot fluid and the other gets cold by fluid which gets heated up. Flows are reversedby auto change-over mechanism which operates inlet and outlet valves of exchangers. They are usedmainly for waste heat recovery from furnace fuel gases for primary air heating for furnace heating.Also in air separation, these are used for cooling of air and removal of impurities in inlet air, whichgets deposited in cold exchanger and in reverse cycle these impurities are removed by hotter air.

2.7 Finned Tube H.EsThe external heat exchanger surface area in finned tube H.Es are increased considerably by

fixing fins arranged either in circular fashion or horizontally along the external diameter of tubes.

2.8 Double PipeThese are used for cooling of hot liquid by C.W. or cold fluid in annular space of the tubes,

which are arranged vertically or horizontally. The fluids flow counter currently.

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30 REFERENCE BOOK ON CHEMICAL ENGINEERING

In Trombone coolers, hairpin type cooling tubes are arranged horizontally and C.W. is asplashed from perforated trough at top and C.W. falls on an open tank below.

2.9 Cascade Coolers for LiquefactionTreated natural gas, after CO2 removal, is usually cooled and methane is liquefied by cascade

process using 3 refrigerants, propane, ethylene and methane successively. Propane has the highestB.P. (–44.5°C) followed by ethylene, (B.P. = –103.9°C and finally by methane (B.P. = –164°C) whichgets liquefied when its temp. falls below critical temp. through 9 stages of cooling. Liquefied propanegets evaporated in propane evaporator by heat from incoming methane gas which evaporates propane(latent heat of evaporation propane is 101.8 Kcal/kg) thereby, cooling methane gas above B.P. ofpropane i.e., –44.5°C; methane is further cooled to above –103.9°C (B.P. of ethylene) by evaporationof ethylene in ethylene evaporator (latent heat of evaporation of ethylene is 125 Kcal/Kg). Finallymethane gets further cooled to below –82.5°C (critical temp.) when it gets liquefied, the pressurebeing above 47.3 Kg/cm2 (critical pressure). The liquid methane gets further cooled to near –164°C(B.P.) by its own refrigeration (latent heat is 121.9 Kcal/Kg) when it is flashed in methane evaporator.The respective refrigerants follow the vapour compression cycle, after coiling process so as toproduce cooled liquid methane i.e., LNG.

3. OVERALL HEAT TRANSFEROverall heat transfer co-eff. for some H.Es have been given in Fig. 1 and 2 for quick estimate

of U. However, it is advisable to calculate U based on first principles. Often a U is considered incalculation followed by confirmatory determination of U.

3.1 Tubes LayoutIn a heat exchanger tubes can be laid out in triangular diamond and square pitches and no. of

tubes in a shell depends on shell dia. and tube pitch. In Fig. 3 calculation for no. of tubes in a ∆pitch and square pitch H.E is given.

4. RADIANT HEAT TRANSFERThe transmission of heat by radiation through space from a surface gas burner to another

cooler surface or gas is governed by Stefan-Boltzman law

Q = F.C 4 4

1 2T TKcal/hr

100 100 −

= F.h (t1 – t2) Kcal/hr.

where, h = Surface (film co-eff. of heat transfer by radiation Kcal/m2.hr.°C

C = Co-eff. of radiation Kcal/m2.hr.(°C)4

F = Area of heat transfer, by radiation

T1 = Temp. °K of hotter body

T2 = Temp. °K of colder body

t1 and t2 = Temp. °C of hotter and colder body respectively

and h =

4 41 2

2

1 2

T TC .

100 100,Kcal/m .hr.°C

t t

− −

Page 42: Reference Book on Chemical Engineering v. 1

HEAT TRANSFER 3 1

The eqn. is useful in calculating fired heaters and furnaces where heat (convection) mode ofheat transfer is also required to be considered. The heat output from burners is to be considered soas to balance the total heat distribution. Also heat loss through wall is to be taken into consideration.

5. HEAT TRANSFER BY CONDUCTIONHeat transfer by conduction takes place within a material (solid, liquid or gas), in majority of

cases a wall is involved and the heat, flowing through it from one face to the other, is given by:

Q = 1 2A . . ( ), Kcal / hr.S

t tλ −

where, A = Area of heat conduction, m2λ = Co-eff. of thermal conductivity of material Kcal/m.hr.°C

t1, t2 = Surface temp. of hotter face and colder face in °C, respectively

Q = Quantity of heat flow, Kcal/hr.

S = Wall thickness m

If the wall consists of no. of layers of thickness S1 and S2 and co-eff. of thermal conductivities,λ1 and λ2, then the heat flow will be:

Q = 1 21 2

2 2

1. ( ) Kcal/hr.

S St t−

+λ λ

6. DATA REQD. FOR HEAT EXCHANGER CALCULATION : CRITERIAA large no. of physical data are reqd. for calculation of a H.E. viz fluid properties–density,

specific thermal conductivities, fouling resistance etc. The design criteria are to be fixed as perprocess requirement. If there is uncertainties in these data, then surface area is calculated byconsidering R-S-S (roof, sum and square) method. In H.E. data sheet often both clean and designover all co-eff. (based on fouling factor consideration) is mentioned and other process and mechanicaldesign data. Apart from shell and tube exchangers, specific equation for film and overall heat transferco-eff. for other types of heat exchangers should be consulted in heat transmission books andPerry’s Hand book. Assumption made should be reasonable. Units of physical properties of fluids tobe correctly ascertained in calculation of U.

7. HEAT DUTYIt is found out from process material balances and heat balance. The C.W. temp. rise is the

limiting point for heat output of an exchanger. The C.W. quality will also determine the fouling factorsto be taken in the determination of individual film co-eff. and overall co-eff. of heat transfer. Anexample of H.E. calculations is given in Chapter 6.

8. SELECTED PROCESS EQUIPMENT DESIGNThis is given in Chapter 6. For condensing vapors, if sensible heat of vapor is required to,

detemrine Q by multiplying flow by latent heat of vaporization, K.

(i) For conversion of U based on o.d. of tube, multiply U by avg

id

d for U based on avarage dia.

of tube. All tube dia. in mm.

Page 43: Reference Book on Chemical Engineering v. 1

32 REFERENCE BOOK ON CHEMICAL ENGINEERING

(ii ) For conversion of U based on i.d. of tube, multiply U by i

o

d

d for U based on o.d. of tube.

(iii ) For conversion of U based on i.d. of tube, multiply U by avg

id

d for U based on avg dia. of tube.

Some H eat Exchanger Types and Average Values for O verall coeffic ient of heat Transfer, U

Type Exchangeconditions

Heat Exchanger w ith Nested Tubes(a) Straight tube

Gas to gas(low pressures)

10–50

Gas to gas at highpressure

100–400

Liquid toliquid

200–1000

Gas at h igh pressure(inner) to liquid

(outer)

200–1000

Liquid to gas(low pressures)

20–70

Number of Passes1 inner (through the tubes)1 outer (round the tubes)

(b) U tube

Internal tube

Tubular shellBaffle

Source : Borsig pocket book 3rd edn. 1970.Fig. 1

Page 44: Reference Book on Chemical Engineering v. 1

HEAT TRANSFER 3 3

Some H eat Exchanger Types and Average Values for O verall coeffic ient of heat Transfer, U

Type Exchangeconditions

(c) H igh-pressure feed water preheater w ithdesuperheating condensation and subcoolingzones on the steam side.

Water (inner) tosuperheated steam

at high pressure(outer)

1500–2500

Gas at h igh pressure(inner) L iquid (outer)

200–500

Gas to gas(low pressure)

10–50(d) Double-tube heat-exchanger

Fig. 2

Gas to gas(high pressure)

Liquid to liquid

100–400

300–1200

Page 45: Reference Book on Chemical Engineering v. 1

34 REFERENCE BOOK ON CHEMICAL ENGINEERING

Number of Tubes in Tubular Heat-Exchangers as a Function ofShell d iametre and Tube Spacing-Triangular

Z

Fig. 3

D’/t Z D’/t

71319313743556173859197109121127139151163169187199211223235241253265271283295301313337349361367379385397409421433439

2.003.464.005.296.006.937.218.008.729.17

10.0010.3910.5811.1412.0012.1712.4913.1113.8614.0014.4215.1015.6215.8716.0016.3717.0917.3217.4417.7818.0018.3319.0819.2919.7020.0020.3020.7820.8821.0721.1721.6322.00

4514634754995115175355475595715835956136256376496616736856917037217337457577697938058178238358478598718778899139259319559679791003

22.2722.5422.7223.0723.5824.0024.2524.3324.5824.9825.0625.5326.0026.1526.2326.4626.9127.0627.5027.7127.7828.0028.2128.3528.8429.0529.4629.6029.8730.0030.2030.2730.7931.0531.1831.2431.4331.7532.0032.1932.7432.8233.05

D ia

D’

60°

D ’ = D – 2at = spacing (betw een tube centres)z = number of tubesD = shell diametre

If D ’/t lies between tw o values, the smaller shouldbe adopted.

For a square nesting pattern w ith the sam e tubespacing, we have approxim ately:

1. W ith the sam e no. of tubes z:(D ’/t) 1.08 (D ’/t)2. W ith the sam e D an hence the same D ’/tz 0.86 z

i

i

i

Source : Borsig pocket book 3rd edn. 1970

Page 46: Reference Book on Chemical Engineering v. 1

HEAT TRANSFER 3 5

Surface in Relation to Heat-Exchanger Length (m /m )2

(referred to external d iameter d of tube (mm) for the fo llow ing nom inal bores d )a i

Fig. 4

71319313743556173859197109121127139151163169187199211223235241253265271283295301313337349361367379385397409421433439

Source : Borsig pocket book 3rd edn. 1970

dd

i

a

2025

2530

3238

4044.5

5057

dd

i

a

2025

2530

3238

4044.5

4514634754995115175355475595715835956136256376496616736856917037217337457577697938058178238358478598718778899139259319559679791003

0.551.021.492.442.913.384.324.795.746.687.157.618.569.509.9710.9211.8712.8013.3014.7015.6516.5817.5018.4518.9319.8820.821.322.223.223.624.626.527.428.428.829.830.231.232.133.134.034.40

0.661.2251.792.923.494.065.195.756.888.018.589.1410.2811.4011.9813.1014.2315.3815.9217.6218.7719.8821.022.222.723.825.025.626.727.828.429.531.832.934.4034.635.736.337.438.639.740.841.3

0.8361.5522.273.704.425.146.577.298.7210.1510.8811.6013.0214.4415.1816.6018.0319.4720.222.323.825.226.628.128.830.231.632.433.835.236.037.440.341.643.143.845.246.047.448.850.351.752.4

0.981.822.664.335.176.017.698.5410.2111.8912.7213.5715.2316.9117.7419.4221.122.823.626.127.829.531.232.833.735.437.037.939.641.242.143.747.148.850.551.353.053.855.557.258.960.561.4

1.2532.333.405.556.627.709.8510.9213.0915.2216.3017.3919.5221.722.824.927.029.230.333.535.637.840.042.143.145.347.548.550.752.953.956.060.462.564.665.767.969.071.173.375.577.578.6

35.436.437.339.240.140.642.042.943.844.845.746.748.149.150.050.951.952.853.854.355.256.657.558.559.460.362.263.164.164.665.666.567.468.468.969.771.672.673.175.076.076.878.8

42.543.644.747.048.248.750.451.652.653.854.956.157.758.960.061.162.363.464.565.166.268.069.070.271.372.474.775.977.077.578.579.880.982.182.683.786.087.187.890.091.192.194.6

53.955.356.759.661.061.863.965.466.768.369.671.073.274.676.177.579.080.481.982.584.086.187.589.090.591.894.696.297.698.399.7101.2102.5104.1104.8106.1109.0110.5111.2114.0115.5116.9120.0

63.164.766.469.871.572.474.876.578.179.981.583.285.787.489.090.692.594.195.896.798.3101.0102.4104.2105.9107.4110.9112.8114.2115.1116.9118.4120.1121.9122.9124.2127.8129.3130.2133.7135.2136.9140.4

z z

Page 47: Reference Book on Chemical Engineering v. 1

36 REFERENCE BOOK ON CHEMICAL ENGINEERINGTe

mp.

Exchange Surface

t : La rge tem perature d iffe rence

t : Sm all tem pera ture d iffe rence

The nom ogram is used for de term ining

the mean logarithm ic temperature difference :

1

2

∆t =m ∆ ∆t t1 – 2

ln ( t / t )∆ ∆1 2

For a para llel or counte r flow hea t-exchanger tand t indica te tem perature d ifference in the fo ll-ow ing m edia at either end o f the hea t exchanger.Re la ted values of t , t , t are joined on thenom ogram by a stra ight line

∆∆

∆ ∆

1

2

1 2 m∆

Fig. 5

∆t1

∆t2

100

90

80

70

60

55

50

45

40

35

30

25

20

15

10

9

8

7

6

5

4

3

2

1

100

90

80

70

60

55

50

45

40

35

30

25

20

15

10

9

8

7

6

5

4

3

2

1

100

90

80

70

60

55

50

45

40

35

30

25

20

15

10

9

8

7

6

5

4

3

2

1

Example

∆t2 ∆tm ∆t1

M ean Logarithm ic Tem peratu re D iffe rence t for Pa ra lle l and C ounter F low H eat E xchangers∆ m

Fig. 6 Source : Borsig pocket book 3rd edn. 1970

Page 48: Reference Book on Chemical Engineering v. 1

37

3Chapter

PULP AND PAPER

1. GRADES OF PAPERThere are several grades of paper depending on and use, type of pulp, pulp usage and wt. of

paper. These are classified as follows:

Type Pulp used wt. in gms/m2

(i) Fine Paper Bleached kraft or sulfite softwoodpulps. Some hard wood pulp is alsoused for opacity.

(ii) News print High mech. pulp and a small % of 48.8chem; pulp.

(iii) Bond paper Bleached chem pulp and cotton fibres 48, 60, 75, 90water marking possible.

(iv) Uncoated soft Kraft or sulfite soft wood pulp withwood paper limited amount of mech. pulp or

recycled paper.

(v) Magazine paper Coated ground wood pulp

(vi) Coated wood Kraft or sulfite soft wood pulp withfree paper coating on both sides. Min 50% mech. pulp.

(vii) Tissue paper Bleached chemical soft wood or hard 15–60wood pulp with some mechanical pulp.

(viii) Wrapping or bag Kraft soft wood pulp 50–134paper

(ix) Cast coated paper, MG. Kraft, high glossy paper.machine glazed

(x) Speciality paper Refined chemical pulp used in electronics,cigarettes, currency making, tea bags etc.

(xi) Linear board Unbleached Kraft soft wood used for 205, 220, 330corrugation.

(xii) Kraft paper Bleached/unbleached from kraft pulpboards

(xiii) Corrugating Unbleached semi chem. pulp and recycled 127medium paper fiber

(xiv) Grease proof From very refined chem. Pulp

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38 REFERENCE BOOK ON CHEMICAL ENGINEERING

2. PAPER SIZE STANDARDS

Size Purpose Wt. in gms/m2

24" × 36" News print 1.6275

17" × 22" Printing 3.7596

19" × 24" Blotting 3.0836

20" × 26" Cover 2.7041

22" × 28" Card board 2.2827

22.5" × 28.5" Bristol 2.1928

25" × 38" Book 1.9801

3. TEST PARAMETERS FOR PAPER(i) Brightness (0 for black to 100% to MgO standard which has on absolute brightness of 96%

by the reflectance of blue light 457 nm from paper)

Burst

Burst index

Stiffness

Flat crush

Tear value

Tear strength

Tensile strength

Toughness index and

Thickness or Caliper (for paper board)

(ii ) Test parameters for wood = Kappa no (indicated lignin in wood) and determines consumptionof oxidation chemical, Pot. permanganate.

4. RAW MATERIALS FOR PAPER MANUFACTURING(i) Soft wood: Fir, Pine, Cedar, Larch, Red wood, Spruce (a type of fir) and some others.

Broadly soft wood contains 55–74% holocellulal (α cellulose 38–50%) and 9–11% pentosans (lignin).Soft wood is obtained from coniferous trees.

(ii ) Hard wood: Birch, Eucalyptus, Maple, Oak, Poplar and some others. Holocellulal contentin hard wood is 70–74% (α cellulose 41–48%) and that of Pentosons is 16–21% (lignin). Hard woodis obtained from deciduous trees.

(iii ) Non wood fibres for pulping: Bamboos, Bagasse, Espartograss, reeds, rice and wheatstraws, ramic and papyrus, corn oat stalks and barley stalks.

(iv) Textile fibres for pulping: Cotton linters, Flam, Manila hemp (abaca) and sisal.

Soft woods are preferred material for pulping due to its longer cellulose fibres (approx. 3–4mm long and dia of 25–30 µ). Low lignin content hard woods are used for special paper makingwhere smoothness and softness are desired.

Page 50: Reference Book on Chemical Engineering v. 1

PULP AND PAPER 39

Table 1Typical analysis of soft wood and hard wood and their pulps.

Constituents Soft wood Hard wood Soft wood Hard wood% wt. % wt. pulp % wt. pulp % wt.

Cellulose 52 54 85 84

Hemicellulose 17 21 12 14(Carbohydrates)

Lignin 28 22 3 1

Extractives (resins, 3 3 - -gums, fats, waxesand colouring matter)

5. MANUFACTURING PROCESSES(i) Pulp manufacturing process principles consists of dissolving cellulosic binding material,

lignin by certain chemical and thus releasing the individual fibres. In the process, extractives are alsoremoved.

The four process steps for wood pulping are:

A. Kraft or Sulfate process at pH 13–14

B. Sulphite process–it is further subdivided into

(a) Commonly used sulfite or bisulfate process at pH 1.5–5.

(b) Neutral sulfite or semi-chemical process at pH 7–10.

(c) Mechanical pulping process.

(d) Chem. Mechanical process using mild action of NaOH or NaHSO3.

Kraft Process is comparatively new chemical pulping process developed in 1940s while SulfiteProcess is the oldest, developed since 1900.

(ii )Chemical pulping stages broadly consist of

(a) Wood preparation

(b) Digestion with reqd. process chemicals

(c) Washing of pulp

(d) Bleaching, washing and screening

(e) Pulp beating

(f) Paper making

(g) Chemical recovery from black or brown spent liquor from digester.

A. Kraft or Sulfate Process5.1 Wood Pre-treatment

Wetted hard wood or a mix of hard and soft wood are cut into 4' or 8' long logs and fed in-to the debrarking mill which consists of rotating large horizontal drum of steel bars. Debarked logis removed from the other end of the drum. Modern method consists of using high pressure waterjets at 1400 PSI at perpendicular to wooden logs for debarking.

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40 REFERENCE BOOK ON CHEMICAL ENGINEERING

The debarked wooden logs are then cut into chips (5/8"–7/8"in length × 1/16"–1/8" thicknessand 1/2"–1") width in a chipping machine.

5.2 DigestionThe chips are then fed into the digester or pressure vessels of capacity 1500-3500 cft and

recovered cooking liquor is added. The composition of kraft cooking liquor is as follows:

NaOH = 70 gm Na2O/lit

Na2S = 30 gm Na2O/lit

Na2CO3 = 20 gm Na2O/lit

The amount of sulfide is defined as “sulfidity” which is Na2S content divided by sum of NaOHand Na2S all expressed as Na2O. Sulfidity is maintained at 25–28%. Na2CO3 present acts as an inertmaterial in cooking liquor after recovery of spent black liquor from digester. Make up Sod. Sulfateis added to black liquor from recovery furnace for use as cooking liquor depending on active materialconc.; caustic efficiency is determined by ratio of NaOH/(NaOH + Na2CO3). In paper mills Sod.sulphate soln. is prepared by melting sulphur with soda ash in air.

2Na2CO3 + 2S + 3O2 → 2Na2SO4 + 2CO2 2H O→ Sod. Sulphate soln.

Pressure in autoclave is kept at 13–14 PSI. Solid consistency in autoclave is 24–30%. Thedigester is heated with steam at 100–115 PSI which gives a cooking temp. at 170–175°C. Digestiontime varies between 4–6 hours. The colour of cooking liquor gradually changes to black as cookingprogresses. Initially dissolution of carbohydrates (soluble hemi-cellulose) is faster than lignin.

After the digestion is over the autoclave pr. (steam) is reduced to 80 PSI and contentsdischarged into a tank. Only 1/2 of Na2S is effectively available.

5.3 Filtering, Washing and Screening of PulpFrom the dumping tank, pulp is separated from spent liquor in cyclindrical washers with

washing of pulp. Screening is done in two stages, firstly in common screen (V.K. roller) that removesundigested chips and secondly in screen which removes uncooked fibres. The pulp output is46–48% of original wood. The colour of Kraft pulp is light greyish brown.

5.4 Bleaching of PulpFor good quality white paper, the pulp thus obtained, is bleached. Initially chlorine bleaching

which was discovered in 1930s is followed by Cl2O and H2O2 bleaching which was introduced adecade later. Oxygenated bleaching agent is used in 1960s. Bleaching is for destruction of chromophorein organic and inorganic compounds remaining in pulp. Bleaching involves oxidation or reduction orboth. The oxidative removal of chromosphore is irreversible, whereas reductive bleaching can bereversible in presence of oxygen in air. Bleaching removes residual lignin from pulp and also purifiescellulose. Now a days bleaching process is subdivided into several steps with washing of pulp inbetween to reduce chemicals. Use of lesser quantities in greater no. of steps reduces danger ofcellulose detoriation by bleaching. Initially less selective chemicals are used and finally selectivebleaching agents are used.

Bleaching is carried out in several towers with washing drums or displacement (diffusion)washers in between the steps. Kraft pulp is difficult to bleach. For bleaching with Cl2 gas or soln.,pulp consistency reqd. is 3–4%.

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PULP AND PAPER 41

Bleaching steps in kraft pulp:

(a) Cl2–alkaline extraction–hypo-chlorite–Cl2O

(b) Same as in (a) followed by alkaline extraction–Cl2O

(c) O2–Cl2–alkaline extraction–Cl2O–H2O2–Cl2O

(d) O2–Cl2–Oxygen/alkaline extraction–Cl2O

(e) H2O2, Cl2O

The no. of steps used for bleaching depends on type of product desired. Paper mills producetheir hypo-chloride by reacting Cl2 with NaOH:

Cl2 + 2NaOH → NaOCl + NaCl + H2O

or Cl2 + Ca(OH)2 → CaOCl2 + H2O

However, use of lime is decreasing. Hydrogen Peroxide is produced by reacting Sod. Peroxidewith water:

Na2O2 + 2H2O → H2O2 + 2Na+ + 2OH–

Chlorine dioxide, Cl2O is an explosive agent. It is gas at STP but explodes spontaneously atpartial pressure of > 40 KPa, decomposing to Cl2 and O2. If heated or exposed to light it canexploded even at lower conc. In paper mills it is usually prepared at site from Sod. Chlorate:

4NaClO3 + 4HCl → 4ClO2 + 2H2O + 4NaCl

2NaClO2 + Cl2 → 2ClO2 + 2NaCl

Bleaching with H2O2 requires stabilishing agent, Sod. Silicate chelating agent (heavy metal ionchelating), dispersants and magnesium salts. Oxygen bleaching is done in NaOH presence.

5.5 Pulp Beating and FiltrationPulp refiners called beaters are used to treat bleached pulp to improve paper making properties.

Originally Jordon/Hollander beaters were used and now replaced by disc refiners. The beater machinelacerate or cut pulp fibres. The disc is made of hardened Ni-white iron. Use of conical disc issubsidising. After wood pulp is diluted to 1.5% congistency and filtered in vacuum filters pulp isobtained. The pulp cake has 10–20% consistency.

5.6 Paper Making through Bleached or Unbleached PulpPurified pulp is used in various paper making machines to produce final paper, dried and packed

automatically.

After beating operation of the pulp, there is large increase in surface area, sliminess, and gooddispersion, increasing in equilibrium moisture/Cu no. and zeta potential.

5.7 Chemical Recovery

The digester spent black liquor pulp and filter washings are treated to recover valuable chemicals,which are reused in digester after addition of make up chemical (Sod. Sulfate). The spent black liquorcontg. 10–15% solids (about 40% inorganic, 60% organic) is concentrated to 48–50% solids in aseries of counter current evaporates (4–6 stages) with vacuum (8–23 mm Hg) at feed end and Pr.operations (45–15 PSI) at outlet end. Tall oil is separated from 2nd stage outlet. The concentrated

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42 REFERENCE BOOK ON CHEMICAL ENGINEERING

liquor contg. 50% solids is black liquor which is further concentrated to 65–73% solids in a heaterand finally sprayed with steam in a recovery boiler using 20% excess air (50% of which is preheatedto 150°C). The organic material in atomized spray dries as it falls and burns and salt gets meltedand flows to the outlet. Air flow is controlled so that all sulphur compounds are reduced to sulfide.Steam is produced in recovery boiler top steam coils.

Make up Sod. Sulfate is added to feed the stream to recovery boiler so that it also reduces toSod. Sulfide. The molten chemical is taken out from the furnace and led into a re-circulating watersettling tank where it dissolves to form green liquor. The dross, about 0.1%, settles at bottom and isperiodically removed. The green liquor is then transferred to causticizing tank where lime is added. Theclear liquid from top is sent to digester and settled lime mud is burnt to make Calcium Oxide for reuse.

Na2SO4 + 4C → Na2S + 4CO

NaOH + CO2 → Na2CO3 + H2O

Na2CO3 + Ca(OH)2 → 2NaOH + CaCO3

Typical data for chemical recovery:

Chemical recovery = 90%

Caustification eff = 85–90%

Reduction of Sulphur Compounds = 90–95%

Steam economy in evaporator 6 stage is possible which will enable 14 lbs of steam at 45 PSIto remove 70 lbs of water from 100 lbs of black liquor containing 15 lbs of solids and 85 lbs ofwater to a conc. of 30 lbs of solids (50% concentration).

6. SULFITE PROCESSThis process differs from kraft process in digestion procedure, bleaching of pulp and chemicals

recovery. Normally soft wood is used.

6.1 Digestion Method and Chemical RecoveryDigester capacity is 3500–12000 cft, chemicals reqd. are sodium sulfite and soda ash. A total

of 6.5% SO2 (free 5.3% and combined 1.2%) is reqd. for digestion to dissolve lignin with theformation of Sulfonate and removal of lignin bonds. Some dolomite is also used. In paper millsSodium Sulfite is prepared by melting sulphur, absorption of SO2 in water to form Sulphurous acidfollowed by reaction with base, NaOH:

S + O2 → SO2

SO2 + H2O → H2SO3

H2SO3 + NaOH → NaHSO3 + H2O

NaHSO3 + NaOH → Na2SO3 + H2O

An alkaline pH upto 10 is maintained in autoclave heated with steam at 80 PSI. Recoveredcooking liquor from chemical recovery section is added into the autoclave after chips are transferred.Cooking time is 7 hrs. Temp. is raised initially to 110°C in 4 hrs. The temp. is again is raised to 135–140°C and kept for 3 hrs. At the end of cooking period, pr. is brought down to 30 PSI and autoclaveeffluent discharged into a pit. After separation of pulp and washing, the grayish white pulp is sentfor bleaching and subsequent operation and the spent brownish liquor is sent for chemical recovery.

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PULP AND PAPER 43

6.2 Chemical RecoverySimilar method for kraft process is used where recovery of chemicals upto 50% is achieved.

The conc. brown liquor is burnt in a recovery boiler. The make up Sod. Sulfite is added to the conc.brown liquor before it is atomized with steam and burnt in boiler. The melt from boller is put in watertank with re-circulation. The green liquor is transferred to causticizing tank where lime is added. Theclarified, filtered clear liquor is then sent to digester for use as cooking liquor. The lime mud isvacuum filtered and cake dried in a rotary kiln to obtain lime, which is reused.

6.3 Bleaching of Sulfite PulpBleaching sequence is as follows:

Chlorine .......... alkali extraction .......... hypo-chlorite

Chlorine .......... alkali extraction .......... hypo-chlorite .......... Cl2O

Chlorine .......... H2O2 .......... alkali extraction .......... hypo-chlorite .......... Cl2O

Oxygen .......... Chlorine alkali extraction .......... Cl2O .......... H2O2

O2/H2O2 .......... Cl2O .......... H2O2

7. MECHANICAL PULPING PROCESSHere, a no. of chemicals are used and the process is suitable for Hard wood and light colored

soft woods, like spruce, balsam, fir and hemlock.

Wet soft wood is debarked, cut into small pieces and ground in a rotating disc to powder form,followed by pulping and bleaching with H2O2. The yield of mechanical pulp is 92-96% of woodtreated. Paper produced is used for newspaper and magazines; very often 30–40% waste paper isused in this process.

Apart from this process, TMP and CTMP processes are also used.

8. DE-INKING OF WASTE PAPERRecycling of waste paper is a very necessary step for conservation of forest products and for

paper manufacture it is essential that ink and other impurities be removed from recycle paper. Thereare two processes:

(i) Wash deinking process.

(ii ) Floatation deinking process.

Both the process involved alkali treatment of waste paper by immersing waste paper basketsin caustic soda solution followed by bleaching with H2O2. Deinked newspaper is used mostly withhard wood pulp for newspaper and magazines.

9. SPECIALITY PAPERHere unused non-wood based raw materials are used to get good quality chemical pulp due to

low lignin content. Leaf cellulose also yields good quality pulp suitable for currency note.

9.1 Bamboo PulpHere NaOH and Soda ash is used as chemicals for pulping. After crushing, the bamboo is cut

into chips and digested with alkali in a two-stage counter current alkali digestor. High quality pulpis obtained which is better than cereal pulp.

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44 REFERENCE BOOK ON CHEMICAL ENGINEERING

9.2 Bagasse and Corn Stalk PulpHere a rod mill is used as a 1st stage digester in series with a 2nd stage digester with alkaline

cooking liquor. High-grade pulp is produced which is suitable for light wt. paper making.

9.3 Cereal PulpHere rice, wheat, oat and barley straws are used as raw materials. Cooking liquor used is milk

of lime (10% CaO) or 13% burnt dolomite. The digester is spherical or rotary. Cooking is carriedout at 115°C for 8–10 hrs. using steam at 45 PSI. The pulp is suitable for corrugated paper.

9.4 Details of Pulp Bleaching (Cl 2 alkaline extraction-Hypochlorite-H 2O2-O2/Cl2O)Normally chlorine bleaching is done with alkali extraction with soda ash at a temperature of

65°C for about an hour and hypo chloride bleaching using Sod. or Cal hypo chlorite at ambient temp.(30°C) for 2–4 hrs. in 2–3 stages with mild alkaline wash in between stages. Subsequent stages ofbleaching are with H2O2. Oxygen and Cl2O are used for better quality paper-making. In all types ofbleaching, calculated quantity of bleaching agent is used. The bleachability test or TAPPI permanganate(O.IN) test indicates amount of chlorine in the form of hypo chlorite reqd. to bleach 100 gm. ofpulp to standard brightness. Actually it measures the amount of 0.1 N KMnO4 soln. that reacts withchlorinated soln., consumed by one gm. of pulp under standard condition.

10. PAPER MAKING BY HOLLANDER MACHINEThe bleached pulp is subjected to beating operation in Hollander machine when cellulosic fibres

swells (expanded) spilt, bruished and deformed. The machine consists of an oval shaped troughdivided in two segments. The bedplate is placed in one section and is made up of projected bars orblades (bronze or steel) of 3/4" dia × 3" thick. A big roller is placed over the blades and bars fixedon the bedplate. The clearance between the roller blades and those fixed on the bedplate is small andcan be adjusted. The roller moves at a peripheral speed of 2000 ft/min. The slurry (5–8% conc.)is circulated around the trough by the padding action of the roller. As the pulp moves through theclearance it is subjected to rubbing, splitting, brushing and deformation along with swelling of thepulp. The clearance is gradually reduced as beating continues. The time of beating varies from 1 hr.to several hrs. depending on the nature of pulp required.

After pulp beating, it is filtered and used for paper making in various automatic machines.

11. Neutral sulfite semi chemical pulping yields black liquor from which acetic acid and formic acidcan be extracted.

Paper pulping liquor is a source of hemi cellulose fraction of wood and from which ligninchemicals can be obtained.

Tall oilIt is obtained from Kraft wood pulping process and it is a mixture of resin and a group of fatty

acids.

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Chlor-alkali industry is one of the key chemicals industry for producing caustic soda (as Pellets,flakes) and chlorine by electrolysis. Pure Hydrogen is produced as a by-products. There are 3processes. Each process uses different method of keeping the Cl2, produced at anode, separate fromNaOH and H2 produced directly or indirectly at cathode. Saturated and purified brine is used at rawmaterial. DC voltage is applied to battery of cells in series.

The cell voltage is kept above the theoretical requirement due to secondary reaction and currentleakages.

(a) Mercury Cell (Castner Kellner Cell-1892)

(b) Diaphragm Cell (Greshiem Cell-1885)

(c) Membrane Cell (1970)

Reactions :

2NaCl + 2H2O → Cl2 + H2 + 2NaOH

Cathode reaction:

2Na+ + 2OH– → 2NaOH

or 2NaHg + 2H2O → 2NaOH + H2(g) + 2Hg

Anodic reaction:

2Cl– → 2Cl– + 2e → Cl2Equation for electrolysis:

Q = I × t

where Q = coulombs of electricity, I = Current in amps, t = time in seconds.

Theoretically 96544 coulombs of electricity will produce 1 gm equivalent wt, which are 35.45gms of Cl2, Hydrogen (1.005) and NaOH (40.01 gm). This output is based on First law of electrolysis(Faraday).

Mercury CellHere Sod. amalgam (NaHg) is produced at cathode which is reacted with water in a separate

reactor called decomposer to produce NaOH soln. and Hydrogen gas and regeneration of Hg takes

4Chapter

CHLOR ALKALI INDUSTRY

45

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46 REFERENCE BOOK ON CHEMICAL ENGINEERING

place. Brine is re-circulated and NaCl salt is reqd. for re-saturation. Brine used is purified-first,dechlorinated and then purified by straight precipitation and filtration process. The products obtainedare very pure. The Cl2 along with little oxygen is used to produce HCl by burning chlorine in air.NaOH contg. little chloride leaves the decomposer with as much as 50% (wt.) concentration. Thisprocess requires maximum power for electrolysis but no steam is reqd. for conc. of NaOH soln.Hg requirement is maximum and requires environmental facility for treatment of Hg leakages fromcell. H2 gas and chlorine must be freed from Hg.

Liberated hydrogen at cathode is carried through electrically insulated pipe from decomposeror cathode compartment and is cooled in a vessel filled with water seal. If Hg and air mixture isformed due to shut down or breakdown, the seal allows the H2-air mixture to escape. A demisteris put to ensure Hydrogen is free from water droplets or NaOH soln. The hydrogen gas is compressedin roots blower or compressor, cooled in an after cooler and sent to consuming points. Hydrogenis about 99.5% pure. The oxygen in hydrogen can be removed by palladium/platinum catalyst andHg by spl. catalyst if necessary for end use. Typical Hg content after cooler in Hydrogen gas is15 mg/NM3 and O2 content is 500 ppm. Cell circuit voltage varies from 1300–2500v and appliedD.C. voltage in each cell is 3.1 volt and operating voltage 4–4.25 volts.

Because of very old process with high consumption of utility as well as Hg loss resulting inHg pollution, this process is obsolete now.

Membrane CellIn membrane cell, anode and cathode are separated by a cation permeable ion exchange

membrane which can be polar or non polar. Here only cations, Na ions and little water pass throughmembrane brings brine purified by de-chlorination and re-circulated which is required for solid NaOHto saturate the brine. Since the life of membrane depends on purity of brine, brine after precipitationfor Mg++ and Ca++, ions are removed by sod. carbonate treatment and filtration. A high purity brineis reqd. It is further purified by ion exchange. NaOH soln. produced at cathode is 35% concentratedand is further concentrated by steam in evaporator to 50% conc. or converted to fused NaOH. Theconsumption of electricity is 25%–40% less than that of mercury cell. The consumption of steamfor conc. of NaOH is also less than diaphragm cell. O2 consumption by electrodes is less. Noenvironmental pollution occurs and the cells are easy to operate. The cells are relatively less costlyand insensitive to current density changes. Power consumption is about 2100 Kwh/Te in the membranecell.

Mercury Cell (Krebs type)

Cathode area = 20.2m2

Cathode size = 14.4 × 1.61 m2

Slope of cell = 1.8%

Current = 300 A

Maxm. Current density = 13 KA/m2

Cell D.C. voltage at 10 KA/m2 = 4.25 V

Stems per anode = 4

Qty. of mercury per cell = 2750 Kg

Energy (DC) reqd. Kwh/Te = 3000

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CHLOR ALKALI INDUSTRY 47

M e m brane

Ano

de

Dep

late

d b

rine

toch

ambe

r (a

nal

yte)

NaO

H s

oln.

to c

ath

olyt

ic c

ham

ber

Cat

hod

ee

lem

ents

Ce

ll

B r ine W a ter

C l ga s2 H gas2

Ano

de

Cat

hod

e

Ce

ll

B r ine W a ter

C l ga s2 H gas2

M e m braneDep

late

d br

ine

toan

alyt

ic c

ham

ber

NaO

H s

oln

.To

cat

hol

ytic

cha

mbe

r

Fig. 1. Membrane cell : Bipolar elements arrangement.

Membrane cell technology came in around 1970. The process is most energy efficient as wellas pollution free.

Saturated pure brine soln. (310 GPI) is fed into anode compartment and water in cathodecompartment of electrolyser where DC voltage above theoretical limit is passed. Sodium ions withsome OH-ions pass through membrane, made of per-fluoro-sulphoric acid or others whose life isabout 4 years and forms NaOH soln. in cathode chamber. Water is added to cathode chamber andNaOH soln. from cathodic cell top is sent to catholyte chamber.

H2 generated, is a very pure type and sent for compression and use elsewhere. The NaOH soln.(~ 35%) soln. form cathodic chamber is sent for concentration.

Chlorine, generated in anodic compartment with oxygen content 0.5–0.7%, is sent for otheruses in the plant of HCl production. Purified brine @ 310 GPI is fed to anode compartment anddeplated brine from anode chamber is taken to anolyte chamber from where it is sent to brinepurification section for saturation with brine soln.

Mono Polar and Bi-polar Electrolyser

Depending on the mode of DC connection to electrolyser cells, they are classified as bi-polaror mono-polar. Bi-polar cells are having min. voltage drops between cells and electrolysers areconnected in parallel. The monopolar cells have simple structure and easy for maintenance. Each cellunit in one electrolyser is connected in parallel and each electrolyser is connected in series of 100electrolysers. Electrolyser operates as per Faraday’s law.

The electrolysers consists of plate type cells. The cathode is made of activated nickel and anodeis of Titanium and both have operating life of 8 years each.

Diaphragm Cell

In this process (also called Nelson Process) the cell is U-shaped with graphite anode at centerand perforated steel cathode covering the outer surface of asbestos, which acts as diaphragm.

The cell is in an outer casing in which steam is put to heat the cell to reduce the resistanceand also to keep the pores of asbestos diaphragm clean.

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48 REFERENCE BOOK ON CHEMICAL ENGINEERING

Purified brine, after causticizing and removal of iron and other metals is kept in the cell atconstant level and electrolysis takes place as it percolates through the asbestos diaphragm.

Cl– ion is discharged at anode as Cl2 and is let off. H+ ions are discharged at cathode whereNa+ and OH– i.e., NaOH accumulation takes place in water which diffuses through porous diaphragmfrom anode compartment. The NaOH conc. is 10–12% and liquor containing NaCl (14–16%) whichis separated by conc. and separates out. The NaOH soln. is further concentrated by evaporation,fused and flaked. No re-circulation of brine takes place. The power consumption is less than mercurycell and product yield contains much NaOH. Actual DC voltage applied in each cell is 3.8 V. Seriescells circuit voltage is 800 V.

Brine Purification Steps

The impurities in brine is given in table 1 below:

Table 1

Sea salt Rock salt

Insolubles 0.1–0.3% ≤ 2%

Water 2–6 ≤ 3

Calcium 0.2–0.3 0.1–0.3

Magnesium 0.08–0.3 0.03–0.1

Sulphate 0.3–1.2 ≤ 0.8

Potassium ≤ 0.04 0.02–0.12

Purification steps for brine depend on type of cells used and impurities in salt (sea or rock).

In membrane and mercury cells HCl is added to brine to lower pH 2–2.23 (Cl2 = 400–1000mg/lit). Brine is sprayed in a packed column or brine sprayed in a vacuum, de-chlorination vesselat 50–60 Kpa which reduces the chlorine conc. to 10–30 mg/lit; vacuum is maintained by steam jetejector or a liq. ring pump. The water from de-chlorinator is condensed in a cooler and furtherreduction in chlorine is done by either activated carbon or chemical treatment with hydrogen sulphite/hydrogen thiosulphite salts. Conc. of sod. chloride is determined by vibration techniques, radioactiveisotopes or density measurement.

Precipitation by adding chemicals

1. With Na2CO3:

CaCl2 + Na2CO3 → CaCO3 + 2NaCl

MgCl2 + Na2CO3 → MgCO3 + 2NaCl

2. With NaOH:

MgCl2 + 2NaOH → Mg(OH)2 + 2NaCl

FeCl2 + 2NaOH → 2NaCl + Fe(OH)23. With Barium Chloride:

BaCl2 + Na2SO4 → 2NaCl + BaSO4

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CHLOR ALKALI INDUSTRY 49

If Mg++ is high in brine, lime soda process is used for its removal which removes Ca also:

MgCl2 + Na2CO3 → MgCO3 + 2NaCl

Mg(HCO3)2 + Ca(OH)2 → MgCO3 + CaCO3 + 2H2O

Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + 2H2O

Ca(HCO3)2 + Na2CO3 → CaCO3 + 2NaHCO3

Dilute solns. of the dosing chemicals are added to weak brine soln. followed by adding freshNaCl salt to bring NaCl soln. to the reqd. level. Brine soln. is further purified by ion exchange resin.

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50 REFERENCE BOOK ON CHEMICAL ENGINEERING

Rayon or artificial silk is regenerated cellulose from cellulose xanthate obtained from xanthationof cellulosic raw materials. Natural cellulose is a polysaccharide (carbohydrate) having the empiricalformula C6H10O5.

There are four main processes for the manufacture of cellulosic fibres or rayon:

(a) Viscose process

(b) Cupraammonium process

(c) Cellulose nitrate process

(d) Cellulose acetate process (non regenerative)

The process at (d) is used in 50% of manufacturing units.

(a) Viscose manufacturing process

Here cotton linters is used as the raw material source for cellulose. The residual cotton left incotton seeds after the lint or cotton has been removed is used for textile manufacture.

The cellulosic raw material thus obtained is subjected to steeping operation using 18% causticsoda soln. at 18°C for 30–90 mins. Excess caustic soda soln. is drained off and the cellulose ispressed until final wt. is about 3 times the original wt. of cotton linters.

Reaction: C6H7O2[(OH)3]n + n NaOH → [C6H7O2(OH)(NaO)2]n + (n–2)H2O

The wet cellulose is then disintegrated in shredders at temp of 20–30°C. Temp. control isimportant as at higher temp. residual caustic will react with cellulose thereby reducing the length ofcellulose chains. The fluffy cellulose material is stored in cans at 25–30°C for 18 hrs., when thelength of cellulose is shortened as per desired length. This ageing process controls the viscosity ofviscose soln., formed at a later stage, and the final strength of finished viscose fiber. Ageing timeand temp. are carefully controlled to achieve desired finished product.

The aged alkali cellulose is then put into revolving drums called barattes each having a capacityof 500–1000 gallons (U.S.) and carbon disulphide is added in the proportion of 50 lbs or less per100 lb of alkali cellulose and reacted for 2–4 hrs. Alkali cellulose is converted to dithiocarbonatecellulose, granular or jelly like mass and the colour changes to bright orange.

5Chapter

CELLULOSIC FIBRES (RAYON)

50

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CELLULOSIC FIBRES (RAYON) 51

Reaction:

This xanthation reaction is exothermic and the barattes are, therefore cooled to keep the temp.at 25–30°C. The gases evolved are also removed. The cellulose xanthate is then transferred to waterjackated dissolvers or mixers in which dil. caustic soda is added along with a delustering agent(Titanium oxide or White Oil) which reduces the brightness of fiber. The cellulose to caustic soln.ratio is maintained at cellulose = 6–9% and caustic = 4–7%. The temp. of this reaction is controlledat 16.7°C. The orange coloured xanthate soln. thus formed is called viscose.

The viscose soln. is then transferred to evacuated blending tanks and allowed to ripen until itbecomes suitable for spinning process for making viscose rayon fibres.

The controlling factors for hydrolysis, carried out in ripening process, are temp., residence timeand ripening process is carried out for 48 hrs. at 17–22°C. Increased residence time or higher temp.accelerates the ripening process.

In the next step, cellulose xanthate is regenerated to cellulose in the spinning bath where it isfiltered and extruded through cup-shaped spinnerets made of Pt-irridium of Pt-gold alloy having holes(0.002 to 0.006 in dia.). For staple fibers, no. of holes could be several thousands. The spinning bathcontains some chemicals also (H2SO4 = 8–12%, Sod. sulphate 0.5–2%, zinc sulphate and glucose).The spinning bath is kept at about 43°C. Sod. sulphate helps in co-agulation in fiber formation andliberation of H2S. Glucose is used to prevent salt formation during precipitation or co-agulationreaction. Sulphuric acid is the regenerating agent which co-agulates the cellulose xanthate and breaksdown the xanthate releasing cellulose. Sod. sulphate is formed in the reaction as also free NaOH isalways present. Zinc sulphate helps which is formed on the filament and increased the tensile strengthin fine filaments.

There are two types of spinning machines–one is pot or bucket type and the other spool orbobbin type. The viscose soln. soon after coming through spinnerets in the form of threads as itpasses through the spinning bath where it is co-agulated and formed into cellulose fiber which travelsupwards through a guide (in bucket type spinning machine, movement is downwards through a feedwheel and then through glass funnel). The revolving bucket speed is 2000–9000 rpm and it givestwist as the bucket rotates. The spinning operation takes 20–30 mins. After spinning, the yarn issubjected to stretching, washing, de-sulphurising, bleaching, finishing (oiling), drying and twistingoperation.

(b) Cuprammonium Process

In cupraammonium process, cotton linters are dissolved in copper hydroxide and ammonium

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52 REFERENCE BOOK ON CHEMICAL ENGINEERING

hydroxide (25° Baume'). The dissolved cellulose soln. is taken to 2nd mixing tank where it is dilutedto 4% cellulose with water–filtered in vacuum filter–blended with other charges and de-aerated. Thefiltered viscose soln. is then pumped to spinning machine where 4% NaOH is used in spinning bath.The yarns are treated with 1–3% H2SO4 followed by washing with soft water and drying.

Raw materials reqd. per lb. of rayon =

Cotton linters = 0.92 lb

Copper sulphate = 0.75 lb

Ammonia = 0.5 lb

NaOH = 0.80 lb

(c) Cellulose nitrate processIn cellulose nitrate process for yarn making, cotton linters are mixed with ether and alcohol.,

filtered and subjected to ageing process.

After ageing the cellulose soln. is subjected to dry spinning. The soln., as it comes out ofspinnerets of spinning machine, it passes through warm air which evaporates the solvents and helpsin coagulation of filament. The individual yarns are combined when a slight twist is given, followedby de-nitration by treating the filament with sod. sulphate or ammonium sulphide soln. The yarn isregenerated into cellulose during de-nitration, washed and bleached.

There is very little use of this process as it is more expensive and dangerous also.

(d) Cellulose acetate processIn this process cellulose is not regenerated but involves the production of cellulose ether. The

process consists of acetylation of cotton linters with combined acetic acid (over 50%) followed byhydrolysis with dil. acetic acid under controlled temp. condition. Water reacts with part of acetylgroup of triacetate liberating acetic acid. When the combined acetic acid content, by hydrolysis, isreduced to 54.5%, the mass is diluted so as to precipitate secondary acetate when entire celluloseacetate is precipitated. This is washed with water to remove acetic acid. The precipitated celluloseacetate is then dissolved in acetone in large enclosed mixers, filtered with stirrers and agitated for12–24 hrs. depending on derived viscosity of cellulose soln. The soln. is then blended in blendinglinks when it is mixed with previous value of quality controlled material. The soln. is then filteredunder press. in cotton filters. Filtration is carried out several times and the cellulose soln. is storedin evacuated vessels for de-aeration.

The soln. is then sent to spinning machine similar to spinning process for cellulose nitrate yarn.The yarn obtained is bright unless some delustreing agent is added in the spinning bath.

Cellulosic Polymers–Rayon, cellulose acetate, cellulose esters, cellophane and modified celluloseare in stiff competition from petrochemicals.

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53

6Chapter

SELECTED PROCESS EQUIPMENTDESIGN

1. Process material balance of the selected process route has to be carried out followed by heatbalance of each equipment calculated with available material balance and various physical dataand data on heat of reactions for various reactions in the process equipment.

A thorough knowledge of reaction kinetics, thermodynamics is essential for designing of achemical process along with types of equipment required for the process route adopted. Similaravailable processes are also to be studied while making material and heat balance.

2. Once material balance and heat balance are ready and checked for Hazop-I (Hazards ofoperations), designing of process equipment starts. Hazop II analysis is to be done after processand equipment design is over and much erection is completed. Hazop III analysis is done withproblems faced during commissioning.

3. A FEW SELECTED PROCESS DESIGN PROCEDURES ARE GIVEN BELOW:3.1 Sizing of Vapour—Liquid Separators

D N D 1

l2

H

N D 2

l1

LD = D iameter of separator, m ml = D m ml = 0.3 DL = l + lH = Ht. of bottom storage of separator, depends on residence time

in secs; For 12 secs residense time, H = 500 mm.ND = Inlet nozzle nom inul d ia, mmNd = Outlet nozzle = ND

1

2

1 2

1

2 1

45°

Fig. 1 Impingement typevapour-liquid separator.

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54 REFERENCE BOOK ON CHEMICAL ENGINEERING

These are impingement type separators used to separate a liquid from vapours from precedingprocess vessels.

Exm: Design a vapour liquid separator for the following gas liquid mixture from the materialbalance of a plant for urea production.

Flow Kg/hr Kg mole/hr

NH3 4094 240

CO2 1377 31.3

H2O 1905 106

7376* 377.3

The gas Pressure is 3 Kg/Cm2 abs at 150°C

Flow of gas Q = 423377.3 22.4 1/3

273× × ×

= 8450 × 0.515 = 4360 m3/hr

= 1.21 m3/sec

Density of gas, Gρ =37376

1.69 Kg/m4360

=

Density of liq. soln. Sρ = 1100 Kg/m3 (assumed)

The theoretical speed of vapour Vt as per Pastonisi’s book, volume-1

Vt = S

G

0.22 1ρ

−ρ

=1100

0.22 1 0.22 25.41.69

× − = ×

= 5.6 ft/sec = 1.71 m/sec.

Design speed, V = 0.4, Vt = 0.4 × 1.71 = 0.684 m/sec.

(40% of Vt)

Free cross-section of the separator assuming 20% oversize :

A = Q/V × 1.20

=21.21 1.20

2.12 m0.684

× =

The separator inside pipe has an o.d equal to

406.4 – 2 × 3.5 = 400 mm

I.D. of separator is =2 2[D (0.4) ] 2.12

4

Π − =

2D4

Π= 0.125 + 2.13 = 2.245

D = 1.905 m = 1900 mm

* Excluding urea wt.

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SELECTED PROCESS EQUIPMENT DESIGN 55

The lower tank part having level indicators is sized for a residence time of 12 secs. l1 isassumed to be D and l2 = 0.3D, and h (assumed) = 500 mm for residence time of 12 secs.

The out following urea soln. from separator, as per material balance is 30904* kg/hr and densityis 1100 kg/m3. The volume of tank (lower) is

V =31.2 12

30904 0.112 m (20% oversize of tank)1100 3600

× × =

Inside diameter of tank:

2 2[ (0.4) ] 0.54

Π φ − × = 0.112 m3

2

4

Π φ = 0.224 + 0.125 = 0.349

φ = 669 say 670 mm

l1 = D = 1900 mm

l2 = 0.3 D = 570 mm,

L (overall length) = 1900 + 570 = 2470 mm

3.2 Sizing of a Steam Heater (H.E)Example: Size up a 13 Kg/cm2 abs. steam heater (steam in shell side) shell and tube heat

exchanger having S.S tube for decomposition of ammonium carbonate soon in tube side. The heatduty required is 2,600,000 Kcal/hr and soln. flow rate is 38000 Kg/hr which is to be heated up inH.E. from 130°C to 150°C.

Calculations–Flow rates in an hour and overall heat transfer co-efficient assumed is 1000 Kcal/hr.m2.°C which has to be verified later.

Heat to be exchanged = 2,600,000 Kcal/hr.

Steam saturated at control valve inlet is 13 Kg/cm2 abs. and effective steam pressure in H.E.(shell side) is assumed 7 Kg/cm2 abs. having condensation temp of 164.2°C.

(a) Calculation of ∆tm:

∆tm = 1 2

1 22.303 log ( / )

t t

t t

=34.2 14.2 20

22.70 C2.303 log 2.41 0.80

− = = °

(b) Exchanger surface area:

Q = U.A. ∆tm

A =Q

U × mt∆

=22,600,000

114.5 m1000 22.7

=× Say 116 m2

* Considering urea wt. in ammonium carbonate soln. undecomposed in preceding steam distiller.

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56 REFERENCE BOOK ON CHEMICAL ENGINEERING

U = 2

1000 Kcal

m .hr.°C (assumed) which will be verified.

Considering 10 × 1.5 tubes, triangular pitch = 15 mm and Tube length of 6000 mm (commerciallyavailable):

No. of tubes = 3

116724 tubes say 730

11 . 8.5 10 . 6− =×

Total pipe cross sectional area

= 2 2730 (0.7) 280 cm4

Π× =

(Considering effective i.d. as 7mm due to fouling.)

Mass velocity in tubes =Flow of soln wt

Sectional area

=238000

135.7 Kg/cm hr280

=

No oversizing considered as steam press. in shell is considered as 7 Kg/cm2 abs.

(c) Velocity of Soln. in tubes:

Soln. flow rate = 38000 Kg/hr

Density of Soln. = 1100 Kg/m3 (assumed)

Volumetric flow =338000

34.54 m / hr1100

=

Pipe passage area = 280 cm2 = 0.028 m2

Velocity of Soln. =34.54

1233 m/hr = 0.342 m/sec0.028

=

(d) Determination of shell inside diameter:

From Table in Borsig Pocket book data in Fig. 3 in Ch-2 we have the eqn. for triangular pitchcorresponding to 730 tubes.

D'

t= 28.21

where D' = C.L. distance of tubes in center line of H.E.

t = tube pitch

D' = 28.21 × 15 = 423.15 mm

Also D' = Di – 2a – tube o.d.

where Di = shell diameter

a = tube o.d.

Then Di = D' + 2a + tube o.d.

= 423.15 + 2 × 10 + 10

= 453.15 mm = 460 mm say.

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SELECTED PROCESS EQUIPMENT DESIGN 57

(e) Baffles:

Segmental cut baffles are considered,

Min. placement of baffles should be 1/5th of shell i.d.

= 1/5 × 460 = 92 mm

Actual baffle spacing considered = 300 mm

No. of baffles =6000

1 20 1 19 nos300

− = − =

(f) φ, (shell dia) = 460 mm

No. of pipes in center =460 460

30.66 say 30pitch 15

= =

Total sectional area of exchanger shell

=2 2(0.46) 0.166 m

4

Π × =

Area occupied by pipes =3 2II

(10 10 ) . 7304

−× × = 0.0573 m2

Passage area of steam in shell = 0.1087 m2

Sectional area for steam passage perpendicular to the tubes is

0.30 (0.460 – 30 × 10 × 10–3) = 0.30 (0.460 – 0.30)

= 0.30 × 0.16 = 0.048 m2

steam flow = 2

2,600,00

Latent heat at 7 Kg/cm

=2,600,00

5264 Kg/hr493.9

=

Sp. Volume of steam a at 13 Kg/cm2 abs.

= 0.1541 m3/Kg

Volumetric flow of steam = 5264 × 0.1541 = 811 m3/hr

Steam velocity perpendicular to tubes:

V =811

4.69 m/sec3600 0.048

(g) Baffle cut (segmental)

AT = 20.1660.048 0.0733 m

0.1087× =

R = 0.230 m

R2 = 0.0529

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58 REFERENCE BOOK ON CHEMICAL ENGINEERING

Heat Exchanger Baffles

(i) Annular Type:

D

d

φi

A = 0.785 ( )a = 0.785 (d)A = 0.785 (D)a = A = 1/3 Ad = / 3D = / 3/2

i i2

2

2

i

i

i

φ

φφ

(ii) Segmental Cut Type:

A tH

R

φi

Baffle spacing should be m in.On shell d ia.

No. of Baffles = Tube Lengthspacing

Area occupied by pipes = xi and Area of id of shell = XFree area = X–xi.Assum e H at 25% or 30% cut, F ind H/R and A /RBasis: Area of passage of shell s ide flu id perpendicularto the pipes shall be nearly equal to area of passage ofshell side fluid paralle l to the pipes.

t2

Fig. 2

T2

A

R=

0.07331.38

0.0529=

AssumingH

R= 0.7

1

H

φ =0.7R 0.7 0.23

0.350.460 0.46

×= =

H = 0.35 × φ1 = 0.35 × 0.46 = 0.161 m say 160 mm

% baffle cut =160

100 34.8% say 35%460

× =

– 1

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SELECTED PROCESS EQUIPMENT DESIGN 59

(h) Verification of overall heat transfer co-eff:

(a) Shell side (steam) film co-eff:

u0 =0.8 0.4

P

0

CD0.023

D

µλ ρ × × × µ λ

v

Re. no. =D ρ

µv

here D0 = 10 × 10–3 m

ρ = 2

1

sp. vol. of steam at 7 kg/cm a

= 3.60 kg/m3

µ = abs. viscosity of steam at 164°C = 0.015 cp

= 0.015 × 10–3 kg/m.sec.

Re. no. =3

3

10 10 4.69 3.6011256

0.015 10

−× × × =

×

Now (11256)0.8 = 0.8 log 11256 = 1742

Pr. no. = PC µλ

here λ = Thermal conductivity of steam

= 0.0199 B.T.U./hr.ft°F

= 0.0199 × 1.488 Kcal/hr.m°C

= 0.0296 Kcal/hr.m°C

CP = Specific enthalpy of satd. steam at 7 ata

= 659.5 Kcal/kg (considered because the steam is condensing)

Pr. no. =3659.5 0.015 10 3600

12030.0296

−× × × =

Now (1203)0.4 = 17.06

0D

λ= 3

0.02962.96

10 10− =×

u0 = 0.023 × 2.96 × 1742 × 17.06

= 2023 Kcal/hr.m2°C

(b) Tube side (carbonate soon) film co-eff:

u1 =0.8 0.3

PD C0.023

D

ρ µλ × × × µ λ i

i

v

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60 REFERENCE BOOK ON CHEMICAL ENGINEERING

Here Di = Tube id, m, 7 × 10–3

v = Vel. of soln. = 0.342 m/sec

ρ = 1100 kg/m3

µ = 0.8 CP = 0.8 × 10–3 kg/m.sec

CP = 0.8 Kcal/kg°C

λ = Thermal conductivity of soln. = 0.45 Kcal/hr.m°C

λ' = T.C. of metal tube

= 14 Kcal/hr.m°C

Re. no. =D ρ

µi v

=3

3

7 10 0.342 11003282

0.8 10

−× × × =

×

(Re. no.)0.8 = (3282)0.8 = 650

Pr. no. = PC µλ

=30.8 0.8 10 3600

5.120.45

−× × × =

0.3P(C )µλ

= (5.12)0.3 = 1.63

Also, Di

λ= 3

0.4564.28

7 10− =×

ui = 0.023 × 64.28 × 650 × 1.63 = 1565 Kcal/m2hr°C

(c) Wall resistance,

t′λ =

33 21.5 10

0.1071 10 m hr°C/Kcal14

−−× = ×

where t = tube thickness, mm

λ' = T.C. of metal wall

(d) Fouling resistance:

Total considered =0.0003 2m . hr . °C

KcalOverall co-eff of heat transfer U,

1

U=

0

1 1total fouling resistance

U Ui

t+ + +′λ

=31 1

0.1071 10 0.00032023 1565

−+ + × +

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SELECTED PROCESS EQUIPMENT DESIGN 61

= 0.00049 + 0.00064 + 0.00010 + 0.0003

= 0.00153

U =21

653.6 Kcal/hr.m .°C0.00153

=

Remarks: Another trial needed with rev. thermal conductivity of steam at 7 ata.

Eqns. for annular baffles, if considered :

No. of annular baffles reqd. =6000

8 1 7750

= − =

Baffle spacing considered = 750 mm

We have, Ai = area of shell

=2 20.460 0.1697 m

4

Π × =

a = area of annulas = 2

4

Π × d

A = area of disc = 2D

4

Π ×

Also a = A = 21 1

A 0.1697 0.0565 m3 3i = × =

d =20.460

0.265 m1.7323

iφ= =

D =20.460

0.375 m1.22493/ 2

iφ= =

For symbols see Fig. 2

(e) Nozzles of H.E

(i) Soln. inlet 38000 Kg/hr

Velocity = 1.3 m/sec

Flow =3 338000

36.2 m / hr (den. = 1050 Kg/m )1050

=

Nozzle size = DN 100

(ii ) Soln. outlet flow as per material balance

= 4360 +330.9

4388 m /hr1.1

=

Velocity = 18 m/sec

Nozzle size = DN 300

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62 REFERENCE BOOK ON CHEMICAL ENGINEERING

(iii ) Steam inlet

Steam flow = 5264 Kg/hr

Sp. Vol. = 0.1541 m3/Kg

Vol. flow = 811 m3/hr

Nozzle size = DN 150

Velocity = 14 m/sec

(iv) Condensate outlet

Flow = 5.264 m3/hr

Nozzle size = DN 150

Velocity = 0.78 m/sec.

3.3 Combustion Calculation for NG Fired Boiler Furnace:Problem–120 ton/hr. steam generation at 90 kg/cm2. Pressure 350°C with NG (mainly CH4)

having NCV = 9001 Kcal/Nm3. Calculate the NG flow rate, gas composition and flow rates for fanand chimney ratings. Consider 80% combustion efficiency.

Enthalpy of steam = 706.9 Kcal/Kg

Total heat in steam = 120 × 103 × 706.9 = 84.83 × 106 Kcal/hr.

NG flow reqd. =6

3 384.3 1011.78 10 Nm /hr

0.8 9001

× = ××

Kg moles of NG burned =311.78 10

525.9 Kg moles22.4

× =

Products flow and composition

Reaction: CH4 + 2O2 = CO2 + 2H2O

1 mole 2 moles 1 mole 2 moles

Reactants Calculation Moles Products Calculations Moles % Dry

CH4 - 525.9 CO2 - 525.9 11.11

O2 (5% 525.9 × 2 × 1.05 1104.4 H2O 2 × 525.9 1051.8 -

excess air)

N2 525.9 × 2 × 1.05 × 79/21 4154.6 O2 2 × 525.9 × 0.05 52.59 1.11

N2 - 4154.6 87.78

Total moles (dry) 4733.09

Total moles (wt.) 5784.89

Expected flue gas composition (dry):

CO2 = 11.11% vol.

O2 = 1.11

N2 = 87.78

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SELECTED PROCESS EQUIPMENT DESIGN 63

Fan and chimmey flow rates considering temp. 25°C:

Methane flow = 525.9 × 22.4 × 273 25

273 0

++

= 12859 m3/hr at 1.033 Kg/cm2 and 0°C

Air flow rate

525.9 × 2 × 22.4 × 100 298

21 273× = 122466 m3/hr at 1.033 Kg/cm2 and 0°C

flue gas (wet) flow rate =5784.89 × 22.4 × 273 210

273 10

++

= 229259 m3/hr at 1.033 Kg/cm2 and 210°C

Fans and blowers need to be sized as above with safety margins.

Dew pt. of waste flue gas:

Partial pressure of water in fuel gas

=1051.8

1.0335784.89

× = 0.1878 Kg/cm2 a

Corresponding to partial pressure of 0.1878 Kg/cm2 a, Dew point from steam table is 58.5°C.

3.4 Run-off Rate of Rain Water in cft/secRamser formula: Q = G.C.A.

where G = rainfall in inches/hr

C = run-off co-eff = run off rate

rain fall rate(1 in 5 or 5 in 10 slope and agri. land, the co-eff is approx. 0.50 or 0.60)

A = area of rainfall acres

Q = Run-off rate, cft/sec

3.5 Bubble Cap Plate TowerFormula for gas velocity per cap

For triangular slots:

V = 0.001068 NC

5/ 20

B 2

2A

gh × ρ

where V = Gas volume per cap, cft/sec

N = No. of slots per cap

C = orifice co-eff (0.51)

W = width of slot, in

A = ht. of triangular slot, in

B = Base of triangular slot, in

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64 REFERENCE BOOK ON CHEMICAL ENGINEERING

ρ = G

L G( )

ρρ − ρ where ρG and ρL are densities of gas and liquid/ft3

g = 32.2 ft/sec2

h0 = slot ht., in

Ref : Cross and Dryder (1952)

3.6 Bernoulli’s Theorem for Determination of Pumping Head Reqd. in Fluid Flow

The theorem is based on the principle of conservation of energy as applied to flow of fluids,between points 1 and 2; the theorem gives the overall equation as:

Static head + velocity head + Pressure head + Friction head

= work input by the pump + external heat input

or, H2 – H1 + 2 22 1V V

2g

− + P2 – P1 + F = W + Q

where, H2 and H1 = static head in ft from an arbitrary horizontal datum

V2, V1 = linear velocity, ft/sec

P2, P1 = Pressure of fluids. lbs/ft2

F = Friction drop, ft of fluid

and W = Work input, ft-lb/lb

Q = External heat input Btu/lb

3.7 Friction Drop is Usually Calculated from Fanning Eqn.

In a circular cross section of pipe at isothermal condition. The determination of fanning frictionfactor, f depends on Reynolds no.

We have, F =2 2

V2

4 LH2 LV 2 LG

D D.D= =

ρc c

ff f

g g

The Reynolds no. DVρ

µ or DG

µ is determined so as to ascertain whether the flow is

turbulent (Reynolds no. > 4100) or the flow is in streamline zone (Reynolds no. < 2100 or in thetransition zone, Reynolds no. in between 2100 – 4100). The friction factor, f is determined fromFanning friction factor chart in Perry’s Chemical Engg. Handbook.

The nomenclature of above equation is as follows:

F = Pipe friction loss, ft of fluid

f = Fanning friction factor as per Reynolds no. fromChart in Perry

L = Length of pipe, ft

V = Linear velocity of fluid, ft/sec

Page 76: Reference Book on Chemical Engineering v. 1

SELECTED PROCESS EQUIPMENT DESIGN 65

G = Mass velocity of fluid lb/sec.ft2

gc = gravitational constant, 32.2 ft/sec2

HV = velocity head, ft

µ = viscosity of fluid at pumping temp. CP/1488 lb/ft.sec

D = pipe dia., ft, ρ = Fluid density, lb/ft3

An alternate simplied formula has been given in Perry’s handbook when Reynold is > 4100 as:

f = 0.0014 + 0.090 0.27

DG

µ

consideration of velocity,roughness factor is reqd.

Often two unknown quantities, viz. pipe dia. and F are involved when a trail and error methodis to be adopted by assuming the pipe dia and then calculation of the F; pipe dia. can be assumedfrom chart for economic pipe dia. chart. The standard equivalent length tables, should be used forfittings.

3.8 Estimation of H.E areas and volume of a vessel when these figures are known for a certainplant capacity for area/volume at some other capacity of an identical new plant by the rule ofthree.

We have the equation,

A2 = A1 × 2

1

S

S

Where, A2 = Area or volume in metric units for new plant of capacity S2

A1 = Area or volume in metric units for known plant capacity, S1

S2 = New plant capacity/annum or day

S1 = Known plant capacity/annum or day

3.9 Estimation of nozzles of equipment of a plant: when plant capacity and nozzle diameter, areknown,

We have the equation,

d2 =2

11

S

Sd

Where, d1 = Nozzle size in mm or inch for known plant capacity, S1

d2 = Nozzle size in mm or inch for a new identical plant capacity

S1 = Known plant capacity or nozzle size

S2 = New plant capacity or nozzle size

3.10 Six Tenth Rule

By this rule approximate estimated cost of a new plant or equipment can be determined basedon FOR/FOB costs when cost of an identical plant or equipment is known.

We have the equation,

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66 REFERENCE BOOK ON CHEMICAL ENGINEERING

C2 =

0.6

21

1

SC

S

×

Where, C1 = Cost of plant or equipment (known capacity or volume) of a known plant orequipment is available

C2 = Cost of plant for a new plant or equipment for an identical plant.

S1 = Known plant capacity or equipment size

S2 = New plant capacity or equipment size.

3.11 Determination of Steam Jacket Pressure of a Crystallization Recirculation Line

We have, Pcr =3 2

3 2

E. ( 1)

12 (1 )

t n

r v

−−

where, Pcr = Limited ext. steam pr. Kg/cm2 a

v = Poisson ratio = 1/3

r = Radius of pipe, cm

E = Young’s modulus, 2 . 1 . 106 Kg/cm2 (steel)

t = Wall thk. of pipe, cm

n = Internal pr of circulating line, (Kg/cm2 a)

Chimney Draught

Static draught hst = H(γL – γG) mm water column (kp/m2)

where H = Chimney height . m

γL = density of air . kg/m3 at tL°C

γG = density of flue-gas. kp/m3 at an average flue-gas temperature tGM°C in chimney

The curves are valid for flue-gases produced by bituminous coal and having a density of

γOG = 1.34 kg/nm3

The cooling of flue-gases in brick chimneys may be assumed to be at the rate of 0.2 °C per metreof chimney height.

For flue-gases produced by brown coal, wood and peat the values shown in the diagram Fig. 3should be multipled by 1.04

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SELECTED PROCESS EQUIPMENT DESIGN 67

0 20 40 60 80 100 120 140

0

10

20

30

40

50

60

70

100

150

200

300

Sta

tic d

raug

ht h

(mm

wat

er-c

olum

n)st

Mea

n flu

e-ga

s te

mpe

ratu

re

Chim ney Height H (m)

400°C

GRAPH FOR CHIMN EY HT

Example : Chimney height H = 80 m

Average flue-gas temperature t Gm = 160°C

Static draught hst = 29 mm water-column (kp/m2)

Source : Borsig pocket book 3rd edn.

Fig. 3

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68 REFERENCE BOOK ON CHEMICAL ENGINEERING

–50 –40 –30 –20 –10 0 20 40 60 80 100

10086

4

2

1086

4

2

186

4

2

0.186

4

2

0.0186

4

20.001

Vapour Pressure of Paraffin H ydrocarbons

Temperature (°C )

E thy lene

E th an e

P ro pa ne

Isob u ta n e

n-Butane

n-Pentane

n-Hexane

n-Heptane

n-Octane

n-Nonane

n -Decane

CH

1226

CH

143 0

CH

1634

Fig. 4

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SELECTED PROCESS EQUIPMENT DESIGN 69

0 2 4 6 8 10 12 14 16 18.0015.0020.0030.0040

.0050

.0060

.00800.01

0.02

0.030.040.050.060.08

0.1

0.2

0.3

0.40.50.60.8

1

V.60t

Q = (–lnp)

= 10

15

20

253040

50607080100

150

200

Evacuation of a Vessel as a Function of Tim e

Time t [m in]

QV

Vac

cuum

p (

ata)

Q = Effective capacity of a vacuum pump, m3/hr.

V = cubic capacity of vessel . m3

t = times . minutes

D = required final pressure . ata (note : ata-atm abs)

Example : A vessel of capacity V = 20 m3 is required to be evacuated in 12 min to a 99.5% vaccum =0.00516 ata. What must the hourly suction volume of the vaccum pump be ?

Pressure and time lines interest at Q/V = 26.4

Required suction volume Q = 26.4.20 = 528 m3/h

Source : Borsig pocket book 3rd edn.

Fig. 5

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70 REFERENCE BOOK ON CHEMICAL ENGINEERING

1. Crude oil, a mix of Paraffinic, naphthenic, aromatic and asphaltic hydrocarbons.

2. The grades are called asphaltic base 60%, paraffinic base 75%, naphthenic base 75% andaromatic base 60% or mixed base according to residue obtained. Other impurities present areSulphur 0.5–3%, Nitrogen 0.1–0.5% and Oxygen compound 0.1–2% as hydrocarbons derivatives.

3. Asphalt or Bitumen is found in crudes, rich in aromatic hydrocarbons.

4. Crudes are also called wax base (>5%), asphalt base (2–5%) and mixed base (<2%).

5. Products from crude oil:

(i) N.G. casing head gas (mix of lighter hydrocarbons upto butane with N2, CO, H2S and higherhydrocarbons.

(ii ) LPG mixture of liquefied Propane and butane (C3 – C4)

(iii ) Natural gasoline (from N.G. by stripping of heavier constituents.

(iv) Straight run gasoline – The yield is for Aromatics crude (6–22%) Naphthenic crude (20-50%), Paraffinic crude (50–70%).

(v) Kerosine – 8–15% C4–C12

(vi) Gas oil (Diesel oil) – C15–C25

(vii) Paraffinic base – C5–C30

Lube oil – Deficient in hydrogen of fused ring type.

(viii) Fuel oil or heavy fuel oil.

(ix) Asphalt or Bitumen.

6. BRIEF CRUDE OIL REFINING PROCESS STEPSVarious products are separated for production of LPG, Gasoline, Kerosine, Gas oil by primary

fractionation of crude oil which is carried out in two stages called stabilization in which crude isdistilled under 3-5 atm pressure to get a top product of C4, C5 and a lighter hydrocarbons responsiblefor giving high V.P and a bottom product. The bottom product is subjected to atm. pressuresecondary fractionation to get light gasoline (B.P. 170°C) as top product and naphthas (med. andheavy) (B.P. 220°C) as side stream product and a bottom reduced crude product which is againdistilled under vacuum (sometimes with steam) to get gas oil and a residue contg. wax cut, lube oil,fuel oil and pitch.

70

7Chapter

PETROLEUM REFINERY

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PETROLEUM REFINERY 71

This residue is further distilled under high vacuum to separate wax, lube oil, fuel oil and pitch/bitumen.

The top product consisting of hydrocarbons upto C5 obtained in stabilization operation is furtherfractionated into individual hydrocarbons (Methane, ethane, propane, N-butane, isobutene, n-pentaneand isopentane.)

The intermediate products in secondary fractionation are subjected to further refinery operationto get purer products or new compounds.

7. CHEMICAL ENGINEERING OPERATIONSystem Physical treatment

1. Liq. Vapour system – Distillation

2. Liq. stream – Extraction

3. Cracking and Reforming thermal – Heat treatment and new compoundand catalytic formation

4. Plat forming – ”

5. Hydroforming – ”

6. Catalytic desulphurisation – ”

7. Alkylation and polymerization – ”

8. Isomerisation – ”

The fuels in conversion process above (3 to 6) may vary from gaseous streams to residual fueloil. The type of intermediate products obtained will vary depending on crude-viz a paraffinic basecrude will give a wax residue containing lube oil and an asphaltic base crude will give asphalt residue.

Cracking and reforming operations are main steps carried out either in vapour or liquid stagethermal or catalytic cracking.

8. REFINERY CATEGORY(a) Simple (b) Complex (c) Integrated types

Simple refinery consists of crude distillation unit, catalytic reforming units and subsequenttreatment plants. The products are mainly LPG gasoline, kerosene and ATF, diesel oils. Kerosine isa mix of light gas oil and heavy naptha.

Complex refinery contains in addition to units in simple refinery, vacuum distillation unit for lubeoils, catalytic cracking accessories units for converting cracked gases to get improved gasoline andATF by alkylation and polymerization or utilization of cracked gases for manufacture of variouspetrochemical and products. The feed gas is naphtha or surplus fuel oil. Bitumen manufacture is alsopracticed. Integrated refinery–it is integrated to produce all types of petroleum products. Thesecontain elaborate vacuum fractionation units for different lube oils and followed by treatment plant,deashphalting units, solvent (furfural) extraction and dewaxing unit. In addition, it contains all unitsin complex refinery.

9. REFORMING PROCESSNaphthas are subjected to catalytic reforming to improve antiknocking property so as to

produce higher octane value in petrol. Process involves heating naphtha under controlled condition

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72 REFERENCE BOOK ON CHEMICAL ENGINEERING

in presence of hydrogen (to reduce coke formation) and a catalyst is used. The process routesavailable are (1) non-regenerative platinum catalyst (0.3–0.7%) platinum on silica-Alumina in H.P.fixed bed multiple reactors. (2) Regenerative non-platinum catalyst (10% moly, or 30% Chromium)in fluidized bed reactors and (3) using cyclic regenerative Pt. Catalyst at moderate pressure (200–300 PSI) in fixed bed multiple reactors.

Crudeoilfeed

Heater

Primarydistillationcolumn

Vacuum towerHeavy gasoil

L ight gasoil

Long residue

Light hydrocarbongases

Gasoline cut

Naptha cut

Bottom product

Secondary distillationcolumn

Fig. 1. Flowsheet for Primary Crude Distillation.

Catalytic Reforming ReactionFeed naphthas are mixture of paraffins and naphthas

nC7H16 = C6H6CH3 + 4H2 ∆H + ve

Paraffins also under go isomerisation, hydrocracking and to a small extent dehydration.

n.C6H14 = Methyl Pentane isomerisation ∆H – ve

C10H12 + H2 = C6H14 + C4H10 ∆H – ve

C8H18 = C8H16 + H2

C6 naphthenes are converted to corresponding aromatics:

C6H12CH3 = C6H6CH3 + 3H2

desulphurisation also occurs

C6H6CH3 + 4H2 = C5H12 + H2S

Fluid hydroforming process is also used.

Non regenerative platinum reforming process is widely used. Thermal reforming process isused for high octane no. Gasoline. Cracking of gas oils and fuels oils either thermally or catalyticallyyields gasoline of higher octane no. using catalytic route; often thermal cracking is also done usingsteam.

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PETROLEUM REFINERY 73

Coking ProcessThe coking process is performed under extreme conditions to manufacture gas, naphtha heating

oil (mazor products) and coke from pitch and tar is used as feed stock. Coke particles and steamare used as fluidising agent. Steam is passed at bottom of reactor to fluidise the bed. Pitch top fedat 260–370°C in the form of a spray from top into the fluidized bed at 480–1270°C. The feed partlyvaporizes and partly collects on the coke particles. The hot pitch on the coke surfaces cracks andvaporizes leaving a non-soluble residue, which forms coke. The vapour coke stream is passed incycles at the top of the reactor where entrained coke is removed. The cracked vapour is then cooledand fractionated when a top product, containing gas, and naphtha, is obtained. The bottom productfrom fluidiser containing heavy tar mixed with residual coke particles is recycled to the cokingreactor.

The stripping and fluidisation steam displaces products vapour from coke surfaces and strippedcoke, then flows to the burner at 590–650°C temp. at 5–25 Psi pressure by burning part of productcoke. There remaining coke is then returned to the reactor. The flue gases are discharged to theatmosphere after separation of coke particles in a cyclone.

Petroleumcoke

Air

Coking reactor

Flare stack

Condenser for furtherfractionation

Gas oil

Recycle

Cokingcham ber

Fluidiser

Steam

Feed(Tar or pitch)

Heavy tar and coke particles

Fig. 2. Flowsheet for Coking Process.

10. DESULPHURISATIONSulphur is removed from low boiling distillates upto 200°C and middle distillates, 250–400°C

are stripped of sulphur by catalytic hydrodesulphurisation process by hydrogen from catalytic reformingprocess or hydrogen generated in the process itself by dehydrogeneration reaction.

Alkylation is done to obtain high octane gasoline from paraffins or olefines.

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74 REFERENCE BOOK ON CHEMICAL ENGINEERING

Lubricating OilsThe long residue after primary distillation of crude oil is subjected to high vacuum distillation

when a short residue is obtained. The long residue constituted asphalt wax, aromatics, naphthenicacid, dark constituents and chemically unstable compound, Good quality lube oil is made by refiningso as to remove these undesireable materials from short residue. The deasphalting step is carried outusing propane. The aromatics and resins are removed by liquid extraction. MEK/Benzene dewaxingprocess or propane dewaxing process are also used.

Sweating process manufactures petroleum wax. Lubrication grease and soap grease are alsomanufactured.

Bitumen soluble in CS2 is obtained from residue from asphaltic and mix base crude when usedfor refining. The primary distillation of heavy long residue is heated to 300°C at atm. pressure.

Page 86: Reference Book on Chemical Engineering v. 1

1. INTRODUCTIONActive carbon has turbostratic carbon structure and a large porous structure with pore diameter

ranging from 1–0.8 nm (less than 2 nanometer) and specific vol. = 0.25 – 0.4 cm3/gm. It hasmicrocystallites–only a few layers in thickness and less than 1000 in width. The surface area is 1000m2/gm due to high porosity, which gives it excellent adsorption capacity. All types of active carbonhas small amount of bound oxygen and H2 in the form of Carbonyl group, Carboxyl, Phenol etc.derived from raw materials. It also contains 20% mineral salts. Convential raw materials give activecarbon a pore size 0.8–1 nm; active carbon from coke gives pore size of 0.5–0.7 nm and molecularsieve active carbon is made from anthracite and it is having pore size of 0.2–0.3 nm. Adsorptioncapacity of active carbon is determined by microscope.

2. MANUFACTUREIt involves charring of raw materials by burning depending on nature of active Carbon desired.

Low carbon raw materials used are coconut shells, saw dust, wood charcoal, bone charcoal, papermill waste liquor. High carbon raw materials are calcined coke/H.T. Coke and anthracite (used formolecular sieves).

When low carbon raw materials are used, it is first charred and formed into briquettes and thenactivated. High carbon raw materials, coal anthracite, are directly activated.

(a) Charring Process – It is partial oxidation of low carbon containing raw materials duringheating at temp. 600–1000°C. The carbon contents is increased to 90%. After charring, the materialis formed into briquettes for activation.

(b) Coking Process – The high carbon raw materials are sized as per requirement and heatedin a furnace in inert atmosphere (oxygen free) using CO2 gas at a high temp. ≥ 1000°C to driveoff all non carbon components of carbonaceous materials using bound oxygen for self oxidation.

3. OXIDATION PROCESSThe carbon materials are then subjected to high gas phase exposure to oxidation atmosphere

(O2, CO2) at about 200°C or alternatively the carbon materials are then treated with conventionaloxidizing agent solution.

4. ACTIVATION PROCESSThere are two processes viz.

8Chapter

ACTIVE CARBON

75

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76 REFERENCE BOOK ON CHEMICAL ENGINEERING

(a) Gas activation and

(b) Chemical activation

There are three variables in activation process:

(i) Nature of starting materials

(ii ) Composition of activation atmosphere

(iii ) Time and temp. of activation process

Item (ii) and (iii ) affect surface chemistry and adsorption by active carbon for various usesand item (i) will give the nature of active carbon product.

Gas Activation ProcessThe carbon after coking or charring is subjected to heating at 800–1000°C in super heated

steam CO2 atmosphere or both. This results in some loss of active carbon. Before heating, usually5% caustic potash or Pot. Carbonate is used to moisten the active carbon charge. This additionaccelerates activation process.

Side reactions H2O + C = CO + H2∆H = 117 KJ

2H2O + C = CO2 + 2H2 ∆H = 75 KJ

CO2 + C = 2CO ∆H = 159 KJ

A high degree of activation gives 20% yield of active carbon whereas a lower degree ofactivation gives 60% yield.

Chemical ActivationIt is done by dehydrating chemicals–starting materials phosphoric acid or ZnCl2–the latter is

used usually for chemical activation of mostly uncarbonised viz. finely divided saw dust and pit coalmixed with phosphoric acid solution when a pulp is formed. This is then heated in a rotary furnaceto 400–600°C; the excess H3PO4 is removed by extraction, neutralized with phosphate salt and driedup. Activation with stream and phosphoric acid also can be done. The dried up active carbon is thencoked or charred. This process is popular and economy depends on recovery or phosphoric acid.

For pharmaceutical use of active carbon low ash content active carbon is made by washingthe activated carbon with water or HCl/H2SO4. Lignite or coal base active carbon when activated byprecise thermal and chemical treatment can prduce carbon with specific pore system.

5. PROPERTIES OF ACTIVE CARBONApart from large pore size distribution and surface area, chemical reactivity of surface area is

important. For many applications of active carbon it does not require to reactivate the spent activecarbon but it is necessary to remove adsorbed material in order to bring carbon to its virgin form.

Adsorption from solution does not involve multilayer formation and depends on chemicalactivity of surface. Adsorption for gas phase purification involves multilayer formation and capillarycondensation in pores of the active carbon. Physical properties of various active carbons are givenin (Vol.-II A).

Regeneration of spent active carbon–It is done by passing super heated steam or inert gasthrough active carbon base, which takes out the adsorbed gases from intergranular spaces. Exhaustedactive carbon from gas purification is heated to red heat for regeneration by decomposing theadsorbed gases and thus desorbing the masses.

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ACTIVE CARBON 77

6. USES OF ACTIVE CARBON1. For liquid and gas purification process–active carbon is used in granular or pelletised form.

2. For molecular sieve, active carbon in proper size is made form anthracite.

3. For water purification and decolourisation, grounded active carbon is used.

4. For food processing, pelletised active carbon is used.

5. Catalyst preparation.

6. Active carbon of high ignition temp. and high resistance to abrasion is suitable for industrialuse for removing sulphur and nitrogen oxides from flue gases from power plant, separation of mixerof gases and in solvent recovery.

7. In gold purification.

8. Active carbon is used in the manufacture of sucrose, glucose, maltose, lactose, soft drinks,edible oils, paraffin wax, phosphoric acid, plasticizers, glycerol, gelatin, pectin, caffeine, quinine,vitamin C, lactic acids etc. Also used in Fruit juices, wine and alcohol manufacture.

9. Powdered active carbon is also used in liquid phase reaction. Grains of active carbon arealso used in gas phase reaction.

10. For odour removal.

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78 REFERENCE BOOK ON CHEMICAL ENGINEERING

There are two types of refrigeration principles used in industry and domestic services:

A. Vapour compression type

B. Absorption type

A. VAPOUR COMPRESSION TYPEIn vapour compression, the refrigeration cycle works on reverse Rankine (or carnot) cycle.

The refrigerant vapour is compressed by a compressor which increases the pressure so that thecompressed vapour attains temp. higher than the cooling water or air and the vapour gives out heatto cooling water/air thereby the vapour condenses to liquid in the condenser as the saturation temp.is reached due to cooling.

The condensed liquid then flows through an expansion valve where partial flashing of liquidtakes place, thus cooling the remaining liquid to below the temp. of product to be cooled. The tempdifference facilitates heat to be transferred from product to refrigerant, which causes the cooling ofproduct and the refrigerant to evaporate. The hotter products give out heat for evaporation ofrefrigerant thereby cooling the product in refrigerated space. Heat of evaporation of refrigerant is thekey factor. For refrigerators, compressor with motor is inside a sealed unit, condensation by air-cooling and refrigerant liquid flashes in freezer body tubes. The vapour of refrigerant is removed bycompressor suction which causes the flow of liquid to maintain and also maintain low pressure inevaporator. The simple circuit given in Fig. 1 and layout in Fig. 2.

RefrigerantsThree types–halogenated hydro-carbons, hydro-carbons and inorganic compounds. These are

generally substances having higher latent heats and low specific heats with the objective of reducingquantity of refrigerant in circulation and minimizing losses, which occur in expansion valve and otherfittings. The boiling point of refrigerant establishes the refrigeration temp. at which it could be usedin the particular refrigeration system. Normally refrigerants are non-inflammable or slightly inflammableand non toxic or slightly toxic.

Coefficient of performance of a refrigerant

It is the ratio ofrefrigeration effect

Works expended =0Q

5.75Q Qk o

=−

9Chapter

REFRIGERATION

78

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REFRIGERATION 79

where Q0 = net heat extracted per unit mass, and

Qk – Qo = work of compression per unit mass

Fig. 1. Vapour compression refrigeration circuit.

This ratio indicates efficiency under certain conditions of the refrigerant selected. It is oftengiven at standard conditions i.e., –15°C (5°F) evaporation and +30°C (86°F) condensation. Themaximum value is 5.75, which is obtained on working with a, reverse Rankine cycle (or Carnotcycle) and is independent of refrigeration. For vapour compression machine, the coefficient is of theorder of three, for air cycle refrigeration application one and for vapour absorption systems, it is wellbelow one.

H.P.

TR=

4.71

eµ (Imp H.P.)

andH.P.

TR=

4.78

eµ (metric H.P.)

Refrigerant Number RIn a numerical cooling system which defines the molecular structure of refrigerant as per

designation ABCD (applicable to halo and hydrocarbons refrigerants only where A, number of doublebonds: B, number of carbon atoms less one, C, the number of hydrogen atoms + one and D, thenumber of fluorine atoms.

Example : For R-12, A = 0, B = 1 – 1 = 0, C = 0 + 1 and D = 2.

Therefore the refrigerant number becomes R-12 (Dichloro Difluoro methane.)

Inorganic refrigerants are designated differently. They are given digits number, the first is 7 andfollowing two numbers gives its molecular number.

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80 REFERENCE BOOK ON CHEMICAL ENGINEERING

b

c

Lay-Out of a Vapour Compression-Type Refrigeration System

EvaporatorBrine (Cold)

Return

O ilSeparator

Cooling water

Cooling water

Condensor

Cooling water

c

f

g

Receiver

(a) F loat value(b) O il collector(c) Safety oil drain(d) Non-condensable gas purging device

(e) Expansion value and charging device(f) L iquid level gauge(g) F ilter

Source : Borsig pocket book 3rd edn. 1970

a

e

RefrigerationCompressor

Suction lineDischarge lineLiquid

Fig. 2

d

Page 92: Reference Book on Chemical Engineering v. 1

REFRIGERATION 81

Example : Ammonia-R 717US’s ASHRAC standard 34–94 (2) classify refrigerants in 6 groups:Group A1 = non inflammable and non toxic.Group B1 = non inflammable but slightly toxic.Group B2 = same as above but moderately toxic.Group A3 = highly inflammable but non toxic.Group B3 = highly inflammable and highly toxic.

Ozone DepletionBoth CFC and HFCs contribute ozone depletion in stratosphere and as a result, ozone hole was

detected in Antarctica. Ozone depletion potential (ODP) has been fixed as 1.0 for CFC–1 and all otherCFCs and HFCs are grouped accordingly.

The production of such ozone depletion compounds was decided to be phased out in 1987 asper Montreal protocol as per the following schedule:

CFCs phase out by 1.1.96 (Developed countries)

HFCs phase out by 1.1.2020 (Developed countries).

However, developing countries were given further extension of 10-15 years from above dates.In view of the above stipulations developed countries are on the look out for alternate CFCs andHFCs. Some HFC refrigerants like R 134 a, hydro-carbons, propane (R-290) and ethane (R-170) arereportedly found better replacements for CFCs and HFCs.

Table 1

Name Code Range Volume refrigerant Effect

Hydro fluoro- R-134 a –15°C evaporation 1062 (KJ/m3)Carbons and 30°C condensation

Ethane R-170 –15°C evaporation 1811 (KJ/m3)and 30°C condensation

Propane R-290 –15°C evaporation 2238 (KJ/m3)and 30°C condensation

Normally mineral oil is used as a lubricant in compressor, which is miscible with refrigerantand return back to compressor for lubrication. About 2–3% lubricating oil is reqd. Details given inTable-5.

However, R-134a requires a synthetic oil, called polyster oil, which is miscible with refrigerant.DIN 51503 gives refrigeration oil specification. For applications of various refrigerants see Table 126in Vol. IIA.

Table 2

Refrigerant TLV. ppm ODP** GWP* 100 yr. Atmospheric Life yr.

CFC-11 1000 1 4000 60

CFC-12 1000 1 8400 130

CFC-13 1000 – 11700 400

HCFC-22 1000 – 1500 15

(Contd.)

Page 93: Reference Book on Chemical Engineering v. 1

82 REFERENCE BOOK ON CHEMICAL ENGINEERING

(Table Contd.)

Refrigerant TLV. ppm ODP** GWP* 100 yr. Atmospheric Life yr.

HCFC-23 1000 0 – 310

HCF-134a 1000 0 1200 16

HFC-152a 1000 0 140 2

Propane (R-290) – 0 3 4

Ammonia (R-717) 25 0 1 1

*Global warming potential

**Ozone depletion potential

Units of RefrigerationIt varies from country to country. Care should be taken as to know the type of refrigeration

unit followed in the country.

A few are as follows:

1 US ton of refrigeration, TR = 200 BTU/min or 12000 BTU/hr

= 3024 Kcal/hr

1 U.K. ton of refrigeration, TR = 220 BTU/min

= 3340 Kcal/hr

1 lb/hr TR = 9 kg/hr per 1000 Kcal/hr

1 lb/min TR = 0.15 kg/min per 1000 Kcal/hr

1 BTU/min TR = 5 Kcal/hr per 10000 Kcal/hr

1 TR (Euorpe) = 211 kg/min

B. ABSORPTION REFRIGERATIONThe system works on continuous basis using ammonia liquor as refrigerant. Separated ammonia

after generator and condenser is taken into expansion coils and dissolved in the absorption vesselhaving water when the pressure falls. The refrigerant is separated by applying heat to refrigeratorand its water content is reduced by rectification, and then liquefied by ammonia condenser usingcooling water and collected in storage tank. The liquid ammonia is passed through expansion coilswhen its pressure falls and partial flashing of liquid occurs with the fall of temp. The flashedrefrigerant cools the cooling media (brine solution) flowing in a coil in the brine cooler. The cold brineis circulated in the storage through coils for lowering the temp. of stored products in storagebunkers/ice plant. The vapour ammonia refrigerant, which absorbs heat from brine solution is thenabsorbed in the absorber and the heat is removed by cooling water. The aq. ammonia is pumped toexchanger and finally the strong aq. ammonia is sent to rectifier for separation of ammonia fromwater. The heat required in the aq. ammonia exchanger is supplied by circulating weak aq. ammoniafrom generator. The process is elaborate and generally finds use in cold storages for vegetables andother products. In place of brine solution, calcium chloride solution is used in some process. Forevaporating temps. of secondary cooling fluids, see Table 127 Vol. IIA for properties of secondarycooling media, Brine soln. (NaCl) and CaCl2 soln; ethylene glycol soln. etc. in vol-IIA. see Fig. 3.

N.B. (i) Safety Precaution-ISO-1662 gives safety precautions to be taken in refrigerationsystems.

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REFRIGERATION 83

(ii ) A heat pump (refrigeration) using a refrigerant having maximum COP in a vapourcompression circuit, pumps out 35 Kw of heat from (say) 7°C to 55°C, will consume 15 Kw ofelectrical energy and gives 50 Kw of heat output.

H

FGBrin e So lu tion

Pd

R

L

h

d

J

J

J

S

E

LRV

D

C

BM

Ab

N

dc

O

Lay o ut of an Absorptio n-typ e R e frigeration system

KRV

i i

g

N H 3Liqu id N H3

Stron g SolutionW eak SolutionC ooling W ate r

d

Fig. 3

A Generator Heating Surface K Solution ReceiverB Analyzer with Rectifier L Solution PumpsC Condenser M RectifierD Liquid Ammonia Receiver N Solution Heat ExchangerE Ammonia Subcooler O Solution Preheater

(Liquid to Gas Heat Exchanger) P Solution ReservoirF Vapour Dome R Auxiliary Solution PumpG Evaporator RV Expansion valveH Solution Collector LRV Solution Expansion valveI Absorber f Flowmeter for liquid ammoniaa Heating steam admission g Drain valve for evaporatorb Condensate Outlet h Screenc Two-cham condensate trap i Non-return valved Liquid Level gaugee Flowmeter for liquid ammoniaSource : Borsig pocket book 3rd edn. 1970.

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84 REFERENCE BOOK ON CHEMICAL ENGINEERING

Table 3Working and Test Pressures (above atmospheric) 1)

as per DIN (Ed of May 1967)

Maximum Admissible Test Pressure Test of finishedWorking Pressure for Individual Installation with

Components Air or Refrigerantswith water

Groups Refrigerant High Low High Low High Low Test PressurePressure Pressure Pressure Pressure Pressure Pressure with LiquidsSide Side Side Side Side Side per ADKp/cm2 Kp/cm2 Kp/cm2 Kp/cm2 Kp/cm2 Kp/cm2 Pamphlets2

Carbon dioxide 95 67 142 100Trichloro-mon- 1 1 1.5 1.5ofluro MethaneR11Dichloro- 13 9 20 13.5difluoro Meth-ane R12

1 Chloro-trifluoro 53 40 80 60Methane R13Difluoro mono- 16 13 24 20chlor Methane 223) 333)R22Trichloro-trifl- 1 1 1.5 1.5uoro ethaneR113Dichloro 4.4 2.6 7 4Tetrafluoroethane R114

Ammonia 16 13 24 20 Same Same 1.3 times223) 333) max. max. max.

2 Methyl chlo- 12 8 18 12 admissible admissible admissibleride working working workingSulphur 9 5.4 13.5 8 Pressure Pressure Pressuredioxide

Ethane 67 50 100 75Ethylene 80 67 120 100

3 Propane 19 12 29 18Isobutane 7 4.6 10.5 7Butane 5.4 3.4 8 5

(1) Lower working and test pressure are possible in low-temperature installations, provided that the whole plant isso designed and protected by safety that there is no risk of the specified pressure being exceeded.

(2) The pressure ratings and test pressure shown in DIN 2401 apply to pipes and fittings. Calculation of wall thicknessas per DIN 2413.

(3) Permitted in high-pressure side under arduous working conditions.

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REFRIGERATION 85

Table 4Physical Properties of Common Refrigerants

Refri- Ethane R 13 Carbon Propane R 22 Ammo- R 12 Methyl R 114 R 11 R113gerant (R170) Dioxide nia Chloride

(R744) (R290) (R717) (R40)

Chemical C2H6 CF3Cl CO2 C3H8 CH2Cl NH3 CF2Cl2 CH3Cl C2F4Cl2 CFCl3 C2F3Cl3Formula

Molecular 30.06 104.47 44.01 44.09 86.47 17.03 120.92 50.49 170.93 137.38 187.39Mass

Gas consta- 28.22 8.12 19.26 19.23 9.81 49.79 7.01 16.80 4.96 6.17 4.525nt Kpm/kg°K

Boiling –88.6 –81.5 –78.5 –42.5 –40.8 –33.4 –29.8 –24.0 +4.1 +23.7 +47.6temp °C at760 Torr

Soldification –183.6 –181 –58.6 –189.9 –160 –77.9 –155 –91.5 –94 –111 –36.5Point °C

Critical temp 32.1 28.8 31.0 96.9 96.0 132.4 112.0 143.1 146 198 214.1°C

Critical pres- 50.3 39.5 75.2 43.4 50.3 115.2 40.9 68.1 33.3 44.6 34.8sure ata**

X = Cp/Cv 1.202 1.15 1.30 1.153 1.19 1.312 1.148 1.27 1.106* 1.124 1.075*at 0°CHeat ofevapora-

tion kcal/ 83.1 25.08 65.3 95.1 52.0 313.5 38.6 100.4 33.88 46.66 38.9Kg at–15°CSpecific vol.of saturated

Vapour 0.033 0.012 0.017 0.156 0.078 0.509 0.093 0.279 0.263 0.772 1.649m3/kgDensity ofLiquid kg/ 0.412 1.12 0.925 0.53 1.285 0.639 1.39 0.96 1.54 0.652 1.62at 0°C

VolumetricRefrigeratingcapacity Kcal/m3 at –15°CEvap. Temp.and + 25°Cupstream ofexpansionvalve 1443 1000 2434 458 519 529 319 307 89.4 51.2 18.3

From “Rules for Refrigeration Machines”, 5th Edition 1958, Veriag C.F. Muller. Karisruhe

*at +25°C **ata = atm.abs.

N.B. For vapour press.–temp. relation of refrigerants see curves in Fig. 7.

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86 REFERENCE BOOK ON CHEMICAL ENGINEERING

Table 5Discharge Temperatures in Single-Stage Compression with Ammonia Compressor

Evaporation Condensing TemperatureTemperature (Discharge Gauge Reading)(Suction Gauge °CReading)

°C 10 12.5 15 17.5 20 22.5 25 17.5 30 32.5 35 37.5 40

+10 10 16 22 28 35 41 47 53 58 64 70 76 82

+5 17.5 24 30 36 43 49 56 62 67 72 79 84 91

+0 26 32 39 45 52 59 65 71 76 82 88 94 100

–5 35 42 48 55 61 68 75 81 86 91 98 105 111

–7.5 40 47 53 60 66 73 80 86 91 96 103 110 117

–10 45 52 58 65 71 78 85 91 96 102 108 114 123

–12.5 50 57 64 70 77 84 91 96 102 108 114 121 129

–15 55 62 69 76 82 89 96 102 108 114 121 127 135

–20 66 73 80 87 94 101 108 115 121 126 127

–25 78 85 92 99 107 113 121 126 132 140

–30 90 97 104 112 120 127 133 140

–40 116 124 133 140

Source: Borsig Pocket Book, 3rd edition 1970.

Power Requirement for Refrigeration Plant using Reciprocating CompressorDiagram 1 of Fig 4 shows the effective power requirement as a function of the refrigerating

capacity of single and two-stage ammonia-compressors on the basis of the following referenceconditions:

(a) Single-stage compressors:

Evaporation temperature –10°C, condensing temperature +25°C;

(b) Two-stage compressors:

Evaporation temperature –40°C, condensing temperature +30°C.

These are average value and apply approximately to other refrigerants also.

Example 1.

Given: Refrigerating capacity Q0 = 600,000 kcal/hr

Evaporation temperature = –10°C corresponding to reference

Condensing temperature = +25°C} conditions for Diagram 1 and 2

Required : Effective power requirement:

From Diagram 1 we have Ne = Nc –10 = 140 KW

Example 2.

Given: Refrigerating capacity Q0 = 600,000 kcal/h

Evaporation temperature = 0°C

Condensing temperature = +32.5°C

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REFRIGERATION 87

Required : Effective power requirement:

From Diagram 1 we obtain the effective power requirement Ne (–10) = 140 KW

From Diagram 2 we find for ±0/32.5°C

Refrigerating capacity = 150%, effective power requirement = 130%

as compared with the reference values –10%, +25%. Therefore effective power requirement

Ne =.140 1.3

122KW1.5

Power Requirement For Reciprocating Compressors for Refrigeration Plant.Diagram 1 shows the effective power requirement as a function of the refrigerating capacity of singleand two stage ammonia compressors on the basis of the following reference conditions:

(a) Single stage compressors:Evaporation temperature –10°C, condensing temperature +25°C;

(b) Two-stage compressors:Evaporation temperature –40°C, condesing temperature +30°C;

There are average values and apply approximately to other refrigerants also

600

500

400

300

200

100

0

0 200 400 600 800 100 0 120 0 140 0 160 0 180 0 200 0 220 0

R efrigerating capac ity Q [10 kca l/h ]03

Effe

ctiv

e p

ower

req

uire

men

t N (

KW

)e

N –1 0°Ce

Q –

10°

C0

D iagram 1

Fig. 4

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88 REFERENCE BOOK ON CHEMICAL ENGINEERING

200

50

100

150

Condensing temperature (°C )

+20

+30 +35 +40

-5

-7.5

-10-2.5-15

-20

-25

Eva

pora

tion

tem

pera

ture

(°C

)

Power Requirement No. [% ]

Ref

riger

atin

g ca

paci

ty Q

[%]

0

200

50

100

150

+10

Power Requirement No. [% ]

Ref

riger

atin

g ca

paci

ty Q

[%]

0

50 100 150 180

C ond ens ing tem pera tu re (°C )

+20 +30+40 +50

Eva

pora

ti on

tepe

ratu

re (°

C)

-30-32 .5

-35-37.5-40

0-45

-50-55

Diagrams 2 and 3 show the percentage variation in refrigerating capacity and effective power requirementfor single-and tw o stage am monia compressors under operating conditions differing from the referenceconditions.

Diagram 2Characteristic curves of a single-stageammonia refrigerating compressor.Reference point 100% :Evaporation Tem perature t = –10°Ccondensing temperaturet° = + 25°C

0

Diagram 3Characteristic curves of a two-stageammonia refrigerating compressor.Reference point 100% :Evaporation Tem perature t = –40°Ccondensing temperaturet = + 30°C

0

+25

Fig. 5. Gives diagram 2 and 3 which shows % variation of refrigeration capacity and effective powerconsumption.

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REFRIGERATION 89

Example : (Cooling water running in series through condenser and absorber):Refrigerating capacity 100,000 kcal/h Heat requirement 220,000 kcal/hEvaporation temperature –20°C (or heating steam consumption 410 kg/h)Cooling water temperature +20°C of heating medium 129°C.Cooling water consumption 16 m3/h Power requirement, solution pump 2.7 KW

Source : Borsig pocket book 3rd edn. 1970.

Fig. 6.

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90 REFERENCE BOOK ON CHEMICAL ENGINEERING

70 50 40 30 20 10 7 5 4 3 2 1 0.7

0.5

0.4

0.3

0.2

0.1

0.07

0.05

0.04

0.03

-100

-95

-85

-75

-70

-65

-60

-50

-40

-30

-20

-10

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2040

6080

100

-90

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R 114

R 21

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R 113

Eth

ane

Page 102: Reference Book on Chemical Engineering v. 1

REFRIGERATION 91

Table 6Procedures for Measuring Refrigerating Capacity

Type of refrige- Type of When Cooling When freezing Tolerancerating Capacity Condenser Liquid Cold Air or ice etc.

rooms Gas Streams

As desired 1 1 1 1 ± 6%9 ± 7%

Overall Refrigera- Water-cooled 2 2 2 ± 5%ting Capacity without evapo- 3 3 3 ± 8%

rative effect

Water-cooledwith Evaporative 3 3 3 ± 8%Effect

Useful 4 7 ± 10%Refrigerating` As disired 5 6 ± 6%Capcity 8 ± 5%

Different procedures are employed for measuring refrigerating capacity, depending on the typeof condenser and the material to be cooled.

By definition, distinction between:

(a) The overall refrigerating capacity, as the product of the refrigerant flow and the enthalpydifference between compressor intake and condenser liquid outlet: and

(b) The useful refrigerating capacity, as the product of the flow-rate (of the refrigerant, coolingmedium, etc.) and its enthalpy difference at two points in the refrigerating plant defined in theContract, at which the cold is utilized.

The individual measuring procedures, together with the tolerances permitted, are shown in thetable 6 above:

1. Measurement of the overall refrigerating capacity Q0 as the product of the refrigerant flowGk and the enthalpy difference;

Q0 = Gk . (i1 – i3)

In this case the refrigerant flow Gk is measured by means of an orifice plate nozzle, meter, etc.Where measurement is made on the gas side, the vapour must be superheated and as free as possiblefrom oil; pulsating flow is avoided. When measurement is made on the liquid side, injection must becontinuous and no displacement of the refrigerant charge must occur.

2. Determination of refrigerant flow from the condenser duty Qc, this being calculated fromthe cooling water flow Gw and the cooling water temperature at the inlet and outlet (tw1 and tw2):

Qc = Gk (i2 – i3) = GwCw . (tw2 – tw1) ± Qu

Using the refrigerant flow Gk thus obtained, the overall refrigerating capacity can be thencalculated by procedure (1).

The term Qu = k.F (tm – tR) is a correction which may be positive or negative depending onthe ambient temperature tR, although as a rule it amounts to only a few percent; for this reason, themean condenser-wall temperature tm, needed on an average, be taken as K = 7 kcal/m2h deg C.

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92 REFERENCE BOOK ON CHEMICAL ENGINEERING

3. Determination of refrigerant flow from the subcooler duty QNK:

QNK = Gk (i3 – i4) = Gw . Cw (tw2 – tw1) ± Qu

The water through flow should be taken as small as possible in order to obtain a minimumtemperature difference of 3°C.

4. Measurement of the flow of cooled liquid Gs and its cooling under steady-state conditions:

Q0 = Gs . Cs (ts1 – ts2)

Measurement of the liquid flow is made by weighing or by flow-metering. At the end of thetest all temperatures should agree as closely as possible with the initial temperatures. Otherwisecorrection must be made using the water equivalent of all components situated within the measuringsection: variations in the temperature difference should, however, not exceed ± 5% of the meanvalue.

5. Measurement under steady-state conditions of the heat required in the cooled liquid to cancelthe refrigerating capacity:

Using steam heating, it is most convenient to weigh the condensate yield Gc per hour. Thecondition ID of the steam as it enters and that of the condensate as it leaves (Ic) must be knownaccurately.

Q0 = Gc (ID – Ic)

Using heating by means of water, having an inlet temperature of th1 and an outlet temperatureof th2, we have:

Q0 = Gh . Cw (th1 – th2)

If the refrigerating capacity is cancelled by means of electrical energy, the current I and voltageU are measured. For direct current, we then have:

Q0 = 0.86 U.I.

6. Determination of the useful refrigerating capacity by heating the cooled space and measuringthe heat required under steady-state conditions:

Stable conditions must be accurately maintained for a sufficiently long period and the coldlosses must be known. This method is thus suitable for refrigerators but not recommended for largecold-rooms.

7. Determination of the useful refrigerating capacity by measuring the air or gas flow GL andthe cooling and drying obtained under steady-state conditions.

Q0 = GL (iL1 – iL2) – GL (XL1 – XL2) iwwhere

iL1, iL2 are the enthalpy of the air at the inlet and outlet, and

iw that of the precipitated, moisture

XL1, XL2 are the water-vapour content at the inlet and outlet.

This method is acceptable only if the conditions, specified in the “Regulations for RefrigeratingMachines”, are observed carefully; no great accuracy should be expected.

8. Ice-production test to determine the useful refrigerating capacity:

Q0 = GE (t1 + 80 – 0.5 tsm/2)

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REFRIGERATION 93

where

t1 is the mean temperature of water when placed in the ice cans.

tsm is the mean brine temperature.

The quantity of ice GE produced per hour is obtained from the weight of the resulting ice-cubesimmediately after removal from the can, not less than 10% of the cubes being weighed on eachoccasion. Strict attention must be paid for the maintenance of steady-state conditions; the brinetemperature at the end must agree exactly with that at the start.

9. If it is desired to determine the overall refrigerating capacity from the ice-product test,proceed as under (8), In addition allowance must be made for the incidence of heat from environmentand for the heat equivalent of the work of the stirrer. The quantity of ice produced per hour is, inthis case, determined by measuring the quantity of water introduced.

Note:The subscripts relating to enthalpy values in the refrigerant circuit are designated as follows (as

per standard rating cycle):The subscript 1 is used for the entry of water, brine, air, etc. and the subscript 2 for their exit.Source: “Rules for Refrigerating Machines”, 5th Edition 1958

Table 7Oils for Refrigeration Machinery

as per DIN 51 503

1. FIELD OF APPLICATIONThis Standard applies to oils suitable for use with evaporation temperatures down to –30°C.

Where even lower evaporation temperatures are involved, special agreements should be made betweenmanufacturer and user and these will often cover testing procedures in addition to maximum andminimum values.

2. TERMINOLOGYRefrigeration-type oils are lubricating oils used in refrigeration machinery and therefore exposed

to the influence of the liquid and gaseous refrigerant.

Note:Oils for lubricating the running gear of open-type refrigeration machinery need not satisfy this

Standard provided that it is impossible for them to enter the refrigerant circuit. Such oils are coveredby DIN 51 501 and DIN 51 504.

3. CLASSIFICATIONRefrigeration oils are divided into two groups to some extent differentiated by the relevant

maximum and minimum values:Group AOil for refrigeration machinery using:Refrigerant NH3 to DIN 8960Refrigerant CO2 to DIN 8960Group B is obsolete, refrigerant SO2 being no longer used

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94 REFERENCE BOOK ON CHEMICAL ENGINEERING

Gruop C

Oils for refrigeration machinery using fluorinated and/or chlorinated hydro-carbons as therefrigerant, e.g.,

Refrigerant R 11 to DIN 8960

Refrigerant R 12 to DIN 8960

Refrigerant R 21 (dichloro-monofluoro methane, CHFCl2) to DIN 8960

Refrigerant R 22 to DIN 8960

Refrigerant R 40 to DIN 8960

Refrigerant R 114 to DIN 8960

4. DESIGNATIONDesignation of a Group A refrigeration-type oil:

Refrigeration-type Oil A DIN 51 503

5. PROPERTIES

Requirement Group A Group C Test as per:

Appearance Clear -

Flash point °C min. 160 Din 51 584

Neutralisation number 0.08Nz, mg KOH/g oil, max. (free of mineral acid and alkali) DIN 51 558

Saponification number 0.20 DIN 51 559Vz, mg KOH/g oil, max.

Ash, weight % max. 0.01 DIN 51 575

Able to flow in U-tube For refrigerationat or below °C machinery with

evaporation temp.betweeen –20°Cand –30°C –30

For refrigeration –25 DIN 51 568machinery with eva-poration temperatureabove –20°C –20

Water content in as- Oils delivered in tank wagons shoulddelivered condition content no settled water after 101 of

the tank contents have been run off.

Oil supplied in drums should containno settled water at room temperature

Oil in small water vapour-tight barrelsshould not contain more than 30 mgof water p.kg.

Resistance to refrigera- - 96 DIN 51 593nts (using R12) hrs.minimum

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REFRIGERATION 95

Matter insoluble in - 0.05 DIN 51 590Freon-12 weight %,max.

Kinematic Viscosity, For refrigeration machinery with DIN 51 561cSt minimum evaporation temperatures between

–20°C and –30°C33 at 20°C 76 at 20°C10 at 50°C 17 at 50°C

For refrigeration machinery with DIN 51 562evaporation temperatures above–20°C –53 at 20°C14 at 50°C

Page 107: Reference Book on Chemical Engineering v. 1

Coal tar obtained from coal carbonization for production of coke, is a source of variousaromatic chemicals and pitch (residue). Coke oven tar is rich in naphthalene and anthracine. The coalgases from coke oven battery or retorts, containing tar and other chemicals are separated in stages.The yields of tar and other coals chemicals depends on type of coal use, mode of coal carbonisationmethod via continuous coke oven battery, retorts as well as type of carbonisation whether hightemperature (1200°C).

Carbonisation or low temperature carbonization (600-800°C) is used. Atmospheric distillationof H.T. coke oven tars yields 50–60% pitch. CVR tar gives 40–50% pitch and tars from L.T.carbonization yields 26–30%

Table 1Composition of crude tars

Item H.T. Coke oven L.T. Coke oven CVR

Yield, Lit/Mt 26–33 75–130 70.9Carbonisation temperature °C 1200 600–800

Density at 20°C 1.169–1.175 1.029 1.074gm/cc

Water, wt% 2.5–4.9 2.2 4.0

Carbon, wt% 90.3–91.4 84 86

H2, wt% 5.25–5.5 8.3 7.5

N2,wt% 0.86–0.95 1.08 1.21

Sulphur, wt% 0.75–0.84 0.74 0.9

Ash. wt% 1.15–1.24 0.10 0.09

Toluene insoluble wt% 5.5–6.7 1.2 3.1

The chief constituent chemicals from coal tar fractionation are benzene and its homologues,phenols, cresols, naphthalene, or carbolic oil, cresols and their homologues and anthracine fromheavy oil (green oil). Tars also contain aniline, pyridine, quinoline and thiophne. Cresols–a pale brownyellowish liquid-become darker with age on exposure to light, contains ortho, meta and para cresols.O-cresols-colourless Deliquescent solid become yellow on exposure to light : m.p. 30°C : m cresolscolourless or yellow liquid : m.p. 10°C. Para cresols-crystalline solid m.p. 30°C. It is a disinfectantfluid.

10Chapter

COAL TAR CHEMICALS

96

Page 108: Reference Book on Chemical Engineering v. 1

Table 2Fractions in continuous H.T. coke oven tar distillation

Item B.P. range °C wt% of crude tar (dry)

Crude Benzol/light oil 99–180 0.5–1.0

Phenolic/Carbolic oil 180–205 3–4

Naphthalene Oil 200–230 10–12

Wash oil (Benzole absorbing 240–290 6–8oil/light creosote oil)

Light Anthracine oil 260–310 12–15

Anthracine oil (heavy green oil) 323–372 95

Residue-medium soft pitch – 53–58

Liquor losses – 4.5

Light oil contains benzene 65% toluene, 3%, ethyl benzene and xylene 8% and remainders arebalance items.

Primary distillation of crude tar upto 150°C yields crude benzole or light oil. Further distillationof crude benzene will yield crude benzene, toluene and xylenes together with some higher aromatichydrocarbons, paraffin, naphthalene, phenol and sulphur and nitrogen compounds. Crude benzene isfurther subjected to hydro refining.

Second product, naphtha and light oil from primary distillation in B.P. range of 150–200°C givesthe important products viz. pyridine bases, naphtha and coumarene resins and creosote oil residue.

Third product naphthalene oil of primary distillation in B.P. range of 200–230°C gives phenolsand naphthalene.

Fourth product wash oil of primary distillation in B.P. range of 240–290°C yields wash oil orbenzene absorbing oil.

Fifth product anthracine oil of primary distillation in B.P. ranges 260–350°C gives lightanthracine oil and heavy creosote oil.

The last fraction, heavy oil is distilled at B.P. range of 323–373°C. The residue is medium softpitch, having softening point (Ring and Ball method) of 60–75°C.

Pitch is a complex heterogeneous mixture of H resins 2.8–14% and M resins 3.8–28.2%.

Table 3

Type of pitch Softening point °C

Refined/base tar below 50°C

Medium soft pitch 60–75°C

Soft pitch 50–60°C

Medium hard pitch 75–110°C

Hard pitch above 140–150°C

Medium hard pitch is made by air blowing of medium soft pitch containing heavy tar oil.Road tar : BS–1964 specifies two types of tar.Type A for surface dressing and Type B for tar macadam. Heavy tar oil bitumen (medium soft

pitch mixture is used as a binder for stone chips in road construction and the viscosity of tar bitumen

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98 REFERENCE BOOK ON CHEMICAL ENGINEERING

should be 50 secs by standard tar viscometer. The disadvantage of road tar is that the temperaturedifference between R and B (Ring and Ball) method of softening point and brittle point is only 46°Cdue to which tar tends to flow in hot weather and suffer from brittleness in winter. Its internalcohesive strength is low. The disadvantage of high temperature coefficient of viscosity can be overcome by blending with petroleum bitumen (pitch). Such medium soft pitch-petroleum bitumen blendsalong with 1–2% PVC or certain synthetic rubber are used in advance countries for road making.

Pitch for Electrode Binder used in AI SmelterA paste of 70% petroleum coke or pitch coke and 30% medium hard coke oven pitch was used

as electrode binder earlier. Now a days, the electrodes after binder appln. is baked at specifiedtemperature.

Refined tar products constitute about 10–12% of crude tar distilled. The bulk product is pitchand creosote oil and blends of pitch and creosote oil i.e., road tar and coal tar fuels.

Table 4Yields of Refined products from tar distillation fractions

Refined Product H.T. Coke Oven L.T. Coke Oven CVR

Wt% dry tar

Benzene 0.25–0.42 0.01 0.22

Toluene 0.22–0.3 0.12 0.22

O Xylene 0.04 0.05 0.06

m Xylene 0.11–0.2 0.10 0.13

p Xylene 0.04 0.04 0.05

Ethyl benzene 0.02 0.02 0.03

Styrene 0.04 0.01 0.02

Phenol 0.5–0.57 1.44 0.99

o Cresol 0.2–0.32 1.48 1.38

m Cresol 0.4–0.45 0.98 1.01

p Cresol 0.2–0.28 0.87 0.86

Xylenols 0.48 6.3 3.08

Tar acids (High boiling) 0.91 12.8 8.09

Naphtha 1.18 3.6 3.21

Naphthalene 9-10 0.65 3.18

α Methyl Naphthalene 0.5–0.72 0.23 0.54

β Methyl Naphthalene 1.32–1.5 0.19 0.68

Fluorine 0.88–2.0 0.13 0.51

Diphenylene Oxide 1.4–1.5 0.19 0.68

Anthracene 1–1.8 0.06 0.26

Phenanthrone 5.7–6.3 1.60 1.75

Carbazole 1.23–1.5 1.29 0.89

Tar bases 0.99–2.00 2.09 2.09

Med. soft pitch 54–60 26.0 43.7

Page 110: Reference Book on Chemical Engineering v. 1

COAL TAR CHEMICALS 99

Tar Distillation ProcessesSmaller size tar distillation plants of capacity 30–70 MT/batch with fractionation column (wt.

10–30 MT) are used in small works while continuous stills of capacity 100–700 MT/day are betterto install.

Crude tar containing NH3 liquor and suspended solids, is first filtered to remove large solidparticle. The liquor is taken into tanks fitted with screen. Some light oil separates by gravity. It isthen heated in a pipe still having a brick lined rectangular chamber divided into a combustion chamberand a convection chamber. In the combustion process, coke oven gas or heavy tar oil or fuel oilis burnt through burners. Hot flue gases are extracted by a blower through apertures in the partitionwall and heat pipe in the chamber, carrying tar.

The exhausted gases are released through the chimney. The heating tar tubes are arrangedhorizontally and parallel to the furnace walls. Normally, heating tubes consist of two separates coils–a waste heat coil and a longer main coil. The waste heat coil is used to heat the tar upto a temperatureto vaporize moisture and light tar oils. The main heating coils may be mostly in convection chamberor partly both in combustion and convection chamber. The tar is finally heated to 360°C whenmoisture and volatile matters get separated from nonvolatile pitch. The separated tar oil is fed to afractionating column where distillation products of increasing B.P. range are separated by fractionaldistillation followed by condensation. Instead of one distillation column a series of column is alsoused. The distillation column has bubble cap type trays, 10-15" apart.

Precaution for Overheating in Pipe StillSince tar on over heating will deposit coke due to decomposition on tube surface resulting in

blockage of flow, the tar is pumped at a back pressure of 10 Kg/sq. cm. The tubes are eitherscreened from radiant heat or use twin tube coils to reduce flux. Flow gas recirculation is also usedto reduce fluegas temperature. Hot pitch can also be circulated with dehydrated tar to reducevaporization and increase flow rate through tubes for better heat transfer.

Corrosion: Free ammonia salt decomposes to HCl after dehydration and decomposition productsof phenol attack carbon steel resulting in corrosion. Use 10% sod. carbonate soln. in crude tar fedto minimize corrosion.

Latest designers for tar distillation plant. 1. Clairton refinery of U.S. Steel Corporation and 2.Teer Verwertung, Germany (Koppers design).

Types of Tar Distillation PlantsMajor differences in plants lie in furnace design in which crude tar is heated, either single pass

with a flash vessel or multiple pass with flash vessel, and using or no using recirculation of residuetar and in the no. of fractionating column and their efficiencies. The processes employing the abovetechniques are called pro-abid, GFT Koppers and Wilton process.

Pro-abid process: In this process, crude tar is screened in a wire mesh, treated with causticsoda soln. and pumped through a series of heat exchangers in the furnace and through waste heatheaters in the convection chamber. The temperature of tar increased to 150–160°C at which the taris fed into hydrator flash vessel where water and light oils are flashed off which are cooled,condensed and water is decanted off from light oil in a decanter. The light oils are then returned todehydrator or in some cases, to distillation column as reflux. The dehydrated tar is heat exchangedwith hot pitch and sent through main furnace coil by a pump and heated to 350–400°C at 2–3 Kg/cm2 pressure and led to a flash vessel. The super heated steam is injected into base of flash chamber.

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100 REFERENCE BOOK ON CHEMICAL ENGINEERING

Remaining volatile oil is degassed from tar. The mixture of steam and volatile oil is fed into fractionatingcolumn from which various fractions are taken off and products separated out after cooling andcondensation.

Coo

lers

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Page 112: Reference Book on Chemical Engineering v. 1

COAL TAR CHEMICALS 101

Refined Products from Tar Distillation1. Primary distillation upto 150°C gives coal tar light oil or crude benzene. Further distillation

of light oil will give benzene, toluene, xylenes together with some higher aromatic hydrocarbon,paraffin, naphthalene and sulphur and nitrogen compounds.

The first stage of refining of benzene or light oil is a defronting process in which steamdistillation is carried out to remove compounds boiling below benzene i.e., forerunnings containingCS2 and some low boiling unsaturated hydrocarbons and paraffins. However, in coal gas works lightoil is less suitable for production of pure benzene or toluene and is used as motor benzol with petrolin some countries where it is allowed. Mild treatment of benzol with sulphuric acid is carried outto reduce sulphur to 0.4% and unsaturated compounds and waste with alkali water before fractioningcolumn.

The defronted benzol is fractionated to produce BTX fractions and heavy fractions and furtherfractionation gives pure benzene and toluene. The fraction is combined with that from first distillationto form zylole/naphtha fraction which is then further fractionated to give various xyloles and naphtha.

However, instead of H2SO4 treatment of benzene, catalytic disulphurisation is also used in someplant, benzene and toluene fractions are made thiophene free and benzene refined to 5–9°C freezingpoint.

2. Primary fraction, distilling in the range of 150–200°C, after further refining gives Pyridinebases, naphtha and coumarene resins.

(a) For Pyridine bases, the distillate is freed from phenols by washing with 10% Na2CO3 soln.The dephenolated oil is treated with 25–35% aq. H2SO4 which reacts with bases to form Pyridinebase sulphate layer separated from waste oil and allowed to stand when resinous matter floats to thesurface. Steaming or boiling removes coextracted neutral oils. The soln. is then cracked by additionalNaOH, soda ash or ammonia when sodium or ammon. sulphate is formed in which pyridine basesare substantially insoluble. The crude basis are separated either by adding solid NaOH or by azeotropicdistillation with benzene and dried.

The dried bases are then fractionated in a column, batch or continuous when various yields areobtained (1) small quantity of pyridine water azeotrope which is returned to drying (2) Pyridine (3)Picoline (4) mix of ρ and γ picoline fraction, and 2,6 lubidine (termed as 90/140) bases) and (5)higher boiling mixture 99/160 and 90/180 bases–the figure 90 indicates 90% distils upto 140°C,160°C and 180°C respectively.

β picoline can be separated by azeotropic distillation with water. The other tar bases occurringin high boiling fractions upto 250°C viz. quinoline, isoquinoline and quinaldin. The quinoline isseparated by fractionation.

β coumarene resin- coal tar naphtha is fractionated to give a narrow boilling range fraction(170–180°C) which is concentrated to coumarene and indene. This is treated with strong H2SO4 toremove unsaturated compounds–washed with water and redistilled. The distillate is heated with acatalyst, usually boron fluoride to polymerize indene and part of coumarene content. Unpolymerisedoil is drained off. The coumarene resin thus obtained varies in colour from pale amber to dark brownand used in paints, polished and flooring colours. The product can also be called indene resins.

Primary distillation range 200–250°C produces fractions of phenol and naphthalene. Here 1stphenols are removed from distillate and then the dephenolated oils are treated for naphthalenerecovery.

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102 REFERENCE BOOK ON CHEMICAL ENGINEERING

(b) Phenol RecoveryThe oil is treated with some excess of 8–10% aq. soda soln. at a temperature just high enough

to prevent naphthalene from crystallising out. The phenols react with NaOH to give crude sod.phenate, phenolate or carbolate. The crude phenolates are separated and the extracted oil, dephenolatedis steam distilled or washed with a solvent to remove neutral oils (1%) and bases (upto 0.5%). Thepurified phenate is decomposed or “sprung” in a tall lower, packed with coke or steel R/Ring,operating counter current to a gas containing 10–24% CO2 or a gas containing 30–37% CO2,specially produced by calcining mix of coke and limestone in a kiln.

The product from bottom of packed tower is separated in a separating tank into two layers-an aq. soln. bottom layer of sod. carbonate and an upper layer of crude tar acid layer. The bottomlayer is drained off.

The crude tar is further refined. Sod. carbonate/bicarbonate is then added to bottom layer fromseparating tank and passed to a recausticizing tank where treatment with quick lime or slaked limeconverts sod. carbonate to caustic soda and precipated CaCO3. The regenerated caustic is recycledfor extraction of crude tar acid from fresh oil.

Subsequent refining of crude tar fraction is done in depitching column which separates oil inthe over head product containing phenol and water and residue of phenolic pitch. The overheadproduct is subjected to vacuum distillation using two or more efficient columns and finally distilledin batch still. The products obtained are pure phenol, pure orthocresol and cresylic acids (mix ofcresols and xylelols).

However, manufacturing phenol synthetically is cheaper.

(c) Naphthalene RecoveryThe dephenolated naphthalene oil contains 85–95% of total naphthalene. There are two processes

for recovery of naphthalene:

(i) Old Process: The naphthalene oil is cooled slowly in open pans to ambient temperature whencrude naphthalene crystallizes and mother liquor is allowed to drain by gravity. The naphthalenecrystals are then centrifuged and then further separated from mother liquor in a hot filter pressureat 400 atm. pressure and temperature of 60°C. This gives a naphthalene of 96% purity havingcrystallization pt. 79–78.5°C. Impurities present are thionaphthlenes which cannot be separated bydistillation or crystallisation and chemical process is used for pure naphthalene.

(ii ) New Process: Naphthalene oil, having paraffines substantially removed, is fed to a dehydratingcolumn where it is mixed with some overhead product from 2nd front column. The dehydratednaphthalene from dehydrator column is passed to front column near top and fitted with bubble capplates. Components boiling below naphthalene are removed as overhead products, part of which issent to dehydrating column. Residue from front column goes to middle of naphthalene fractionatingcolumn. The top naphthalene product is of hot process quality. The bottom product together withreminder of overheads from front column is allowed to cool in pans. The crude naphthalene crystalsare drained off from pans and recycled with fresh feed.

(iii ) Pure naphthalene by chemical process: The liquid naphthalene (96%) is agitated with 10%of 94–95% H2SO4 and washed with water and alkali and further distilled in a naphthalene columnwhen 99% naphthalene is obtained which is cooled, crystallised and filter pressed to get solid purenaphthalene having crystallisation point of 79–80°C.

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103

There are various types of refractory bricks:

1. Silica bricks

2. Dolomite bricks

3. Chromite bricks

4. Chrome-Magnesite bricks

5. Alumina-Silicate bricks

6. Sillimanite bricks

7. High alumina bricks (70%)

8. Low alumina bricks (42%) or fire bricks

9. Magnesite bricks

10. 54% silica fire clay bricks

Properties, uses and raw materials for refractory bricks:

(i) Silica BricksBulk density = 1.73–1.78 gm/cc

Porosity = 22–25%

Temperature = 1710°C

Uses : O.H.F. roof lining

Molasses or sulphite lye is added to ground raw materials before moulding of bricks to increasegreen strength. Sulphite lye is from paper making sulphite process.

(ii ) Dolomite Bricks CaMg (CO 3)2

Dolomite is a mixture of Ca and Mg oxides, 25% CaO and 21% MgO. On heating the reaction

is : CaMg(CO ) CaO + MgO + 2CO3 2heat

2 →

Properties of dolomite bricks:

Bulk density = 2.52–2.58 gm/cc

Temperature = 1300°C

Uses : In cupola and rotary kiln.

REFRACTORY BRICKS

11Chapter

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104 REFERENCE BOOK ON CHEMICAL ENGINEERING

(iii ) Chromite BricksAvg. composition of Indian chrome ores,

SiO2 = 1.27% CaO = 0.57

Al2O3 = 12.75% MnO = 13.51

TiO2 = 0.37% Cr2O3 = 45.33

FeO = 7.12% CO2 = 0.22

Fe2O3 = 15.97% H2O = 2.67

Properties of chromite bricks:

Bulk density = 3.10 – 2.84 gm/cc

Porosity = 22%

Temperature = < 1250°C

Uses : Steel, O.H. (non ferrous), Cu converter

(iv ) Chrome–Magnesite BricksProperties of chrome–magnesite bricks (> 50% chrome):

Bulk density = 2.92–3.0 gm/cc

Porosity = 25–23%

Temperature = < 1300°C

Uses. Open hearth furnace, re-heating furnace hearth and soak pits.

(v) Alumino–Silicate Bricks (38.1% Alumina and 57.8% SiO 2)

Raw materials, bauxite and fire clay

Properties of alumino – silicate bricks:

Bulk density = 1.85–2.5 gm/cc

Porosity = 30–24%

Temperature = 1580°C

(vi ) Sillimanite (Al 2O3, SiO2) BricksProperties of sillimanite bricks:

Bulk density = 2.4–2.47 (A10) and 2.5–2.58 gm/cc

Porosity = 9–13% (ASTM – A10) and 12–16% (ASTM A11)

Temperature = 1980°C

Sillimanite mineral is found in Khasi hills of Meghalaya in India.

Uses: Glass melting tank lining.

(vii) High Alumina Bricks (70%)Raw materials, 98% Bauxite and clay

Properties of high alumina bricks:

Bulk denisty = 2.9–2.96 gm/cc

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REFRACTORY BRICKS 105

Porosity = 14 – 18% (ASTM C4)

Temperature = 1700°C

Uses: Steel plant

(viii) Alumina Bricks (42%) or Fire BricksProperties of alumina bricks:

Bulk density = 1.97 (BSI code C4) gm/cc

Porosity = 19 – 22.1%

Temperature = 1575°C

Uses. In acid Bessemer tuyers, non ferrous and glass melting furnaces and coke ovens etc.

(ix) Magnesite BricksProperties of magnesite bricks:

Bulk density = 2.86 gm/cc

Porosity = 14.5 – 19.8%

Temperature = >1730°C

Uses. Mostly used where resistance to strongly basic slags is required, under hearth and liningof O.H.F. and re-heating furnace.

(x) Fire Clay Bricks (54% SiO 2)Properties of fire clay bricks

Bulk density = 2.16 gm/cc

Pprosity = 16.5%

Temperature = 1680°C

Uses: Excellent general purpose bricks for re-heating furnaces, furnace doors, boiler soakingpit etc.

(xi) Mullite Bricks (65 – 75% Al 2O3)Properties of mullite bricks:

Bulk density = 2.55 gm/cc

Porosity = 17 – 23%

Temperature = 1750°C

Table 1Thermal Expansion of refractory bricks

Type of bricks % Thermal expansion Clearance expansion(200 – 1000°C) in laying

Fire Clay bricks 0.5 – 0.7 1/16" – 3/32" per ft.

Chrome bricks 0.8 – 0.9 5/32" per ft.

Chrome-Magnesite bricks 0.8 – 0.9 3/16" per ft.

Dolomite bricks 1.3 –

Silica bricks 1.2 – 1.4 1/8" – 3/16" per ft.

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106 REFERENCE BOOK ON CHEMICAL ENGINEERING

Shapes of Refractory BricksVarious sizes and shapes – One size is L = 9", W = 4.5" and thickness = 3"

GLOSSARYFlux – A chemical, which lowers the fusion point of a refractory material.

Grog – Non plastic materials, usually prefired and added to bricks to reduce drying and firingshrinkages or to obtain special properties i.e., high thermal shock resistance.

Porocity – Ratio of volume of pores in a refractory body to the volume of entire body andexpressed in percentage.

Plasticity – It is the property of a material by virtue of which it can be shaped (moulded) intoany form and which can be retained when the pressure of moulding is released.

Green strength – The strength of ceramic body in moulded but unfired state.

Modulus of rupture – Transfer strength of material.

Eqn. M =3 wl2 bd2

where w = total load, lb.

l = distance between supports, inches

b = width of test pieces inches

d = thikness of test piece, in

M = MOR, lb/in2.

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An explosion is a violent noisy outburst accompanied with sudden build up of high pressureand release of pressure associated with a chemical change liberating heat and light.

GASEOUS EXPLOSIONA gaseous explosion is generally non-detonation type which takes place (i) when the flammable

or explosive mixture is within the flammable limits i.e., in between lower and upper limits ofexplosion in air and (ii ) a source of ignition in the form of (a) hot surface or (b) electric spark or(c) spark due to friction (d) naked light or (e) ignition by shock waves.

Lower the explosive limit, greater is the explosive energy release. At near higher explosive orflammable limit, the mixture burns with long flame. The ignition temperature of a flammable vapouror gas depends on pressure of the gas itself. The ignition temperature decreases as the pressure ofgas/vapour increases.

EXPLOSION DUE TO PRESSURE VESSEL RUPTUREIt is a mechanical failure of vessel under pressure due to excessive pressure or corrosion,

resulting in thinning out of vessel wall/heads and the metal is unable to bear the tensile strengthrequired to withstand the internal pressure of the vessel. Since it is a physical explosion, no chemicalchanges occurs and release of heat and light do not occur. However, for a chemical plant, the fluidshandled in many cases are flammable, which may cause generation of sparks due to friction of flyingmetal objects from the ruptured vessel and its supports, hitting other objects in vicinity, causingsparks and ignition of gases, if flammable.

DETONATIONIt is caused by mere impact or detonation shock waves or electric sparks. Powerful explosives

or explosive gases having lower limit of flammability producing shock waves having very highdetonation speed, sometimes as high as MACH 10 (10 times speed of sound), due to violent changes.The speed of shock wave is above 330 m/sec or so. In the case of ethane-air mixture, the flamevelocity is 63 cm/sec and detonation wave speed is 1734 m/sec. In detonation, shock wave initiateschemical reaction which propagates through the explosives charge. Detonation is carried forwardon the peak of a shock wave. Gaseous detonation is dependent on pressure, volume, energy andvelocity and also the time taken for detonation. For an explosion to occur, the reaction must beexothermic. A fraction of chemical energy is used to propagate a shock wave.

12EXPLOSIVES AND DETONATORS

Chapter

107

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DETONATORSThese are devises viz. a small amount of very sensitive primary explosive charge is embedded

in a high explosive material and mechanical or electrical devices used to set off the main highsecondary explosive. Often fuse wire is used for detonation, which consists of a train of black gunpowder wrapped in tube of tissue paper or a woven waxed fabric. In mining, high explosive fusewire is used. Often the blasting cap of a detonator usually contains a small charge of PETN totransmit a powerful shock wave, ignited by fuse wire and serves to touch off the primary explosive.

Gas detonation velocity is calculated from the following formula:

Det. Velocity = V1 tanθwhere V1 = volume of detonating gas

tanθ = angle of tangent to equilibrium line with no reaction curvefor detonating as per Hogoniot curve for the particulardetonating gas.

Gasoline has a detonation velocity of 1/106 meter/sec, for high explosive it is 6000–8000 m/sec and solid propellant 1/102 m/sec. The detonation pressure may rise upto 200,000 atm. in caseof high explosives.

Table 1

Gases and other Calculated detonation Actual detonationvelocity, m/sec velocity, m/sec

2H2 + O2 2806 2819

2H2 + O2 + 5N2 1810 1822

C2H2 + O2 2960 2920

Nitroglycerine 81 80

(liquid)

TNT (solid) 6480 6700

CATEGORY OF EXPLOSIVES

EXPLOSIVES FOR INDUSTRIAL USESBlasting gelatine – 8% nitrocellulose in nitroglycerine (mining)

Other explosivesTNT – Trinitro toluene; Amatol–Ammon. nitrate and TNTANFO – Ammon. Nitrate – fuel oil mixture (IED), Nitroglycerine [C5H5O9N3 (Liq)]RDX – Research and Development explosive, Hexogen or cyclonite

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EXPLOSIVES AND DETONATORS 109

PETN – Pentaerythritol tetranitrate

HMX – Cyclotetra methylene tetra nitramine

HMS – Hexa nitrostilbene

TATB – 1, 3, 5 triammino –2, 4, 6 trinitrobenzene

TNP – Trinitro phenol

Tetryl – (NO2)3 C6H2N(NO2)CH3 also known as Tetralite

N.B. RDX is used with wax or TNT due to high sensitive nature. Chemical name of RDX iscyclo trimethylene trinitramine.

Table 2Properties of Explosives

Name M.P. V.P. Crystal Detonation Lead blockO°C Pa density gm/cc velocity m/sec test 10gm, sm3

Nitroglycerine 13.5 1 1.591(liq.) 7700 520

RDX 204 0.05 1.82 8850 480at 110°C

TNT 80.8 6 1.654 6960 300

PETN 141.3 0.1 1.77 8340 520

HMX 283 – 1.907 9100 520

TATB 7550 – 1.94 7970 –(decom.)

TNP 122.5 1 1.767 7500 315

Tetryl 129.4 – 1.73 7570 –

Some Primary ExplosivesMercury fulminate

Lead azide

DDNP (Diazodinitro phenol)

Ammonium nitrate

Table 3Impact Sensitivity of Secondary Explosives

Insensitive Value

TATB 72.5

TNT 1

Moderately Sensitive

TNP 0.7 – 0.9

Tetryl 0.4

HMS 0.6

(Contd.)

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110 REFERENCE BOOK ON CHEMICAL ENGINEERING

(Contd.)

Sensitive – high explosive

HMX, RDX 0.3

PETN 0.15 – 0.2

Nitroglycerine 0.1

Functional groups in explosives

(a) Nitro gr. – Salts of HNO3, derivatives etc.

(b) O nitroderivatives – nitroesters (RONO2) – PETN

(c) C nitroderivatives – aliphatic and cryclodiphelic nitrocresols

(d) N nitroderivatives – RDX and HMX

TREND IN THE USE OF BLASTING EXPLOSIVESBoth nitrocellulose and nitroglycerine are mixed in tankers and pumped to boreholes in open

cast mines and detonated using fuse wires.

Riot Chemicals – These are CN (chloroacetophenone), CS (ortho chlorobenzol metanitrite) andDM (Diphenyl amino chloroarsine) – the latter being more effective than CN or CS. Riot chemicalscause skin irritation. Tear gas contains lacrimating compounds (watering of eyes) viz Bromo acetone,benzyl chloro acetone, ethyl iodoacetate etc. usually put in explosive shell which on firing gives outaerosol of lacrimating compounds.

Plastic Explosive – A combination of petroleum jelly, latex and RDX, designated as C-C4 andcontaining 88.3 to 91% RDX and plasticiser varies from 11.7% to 20%, 22% and 9% (C2 to C4).

Gelatin Dynamite – It contains mainly gell like mass of nitroglycerine with sodium nitrate, meal,cotton and sodium carbonate. This high explosive can be detonated by fuse wire or a timer orwireless signal.

Chemicals of Mass Destruction (CMDs) – SARIN, a nerve gas consists, mainly methylphosphonofluoridic acid and ethyl ester. Mustard gas is a blister gas, which acts as a cell irritant andcell poison. CMDs are banned by international treaty.

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1. GENERALWater occurs abundantly in nature as rain water (from evaporation of water) surface water

(lake, river and sea), underground water and spring water. However, water has great solvent propertyand as such it cannot be used unless suitably treated for use as potable water or process water orboiler feed water. Pure water ionizes to a small extent and its conductivity at 18°C is 0.044 µs/cm.Rain water, after first showers is very pure like distilled water. Underground water, which occursin sandy layer is clear and free from organic impurities and nitrogen compounds which are oxidizedby soil bacteria. Spring water contains some special constituents.

2. IMPURITIESWater, depending on source, contains floating objects, fine silica (silt) which impart turbidity,

dissolved salts of Ca, Mg, Iron and often Manganese. These salts are present as bicarbonates,Ca(HCO3)2, Mg(HCO3)2, Fe(HCO3)2 ferrous bicarbonates, as sulphates, CaSO4 and MgSO4; aschlorides CaCl2 and MgCl2 or as nitrates Ca(NO3)2 and Mg(NO3)2. Presence of bicarbonates givescarbonate hardness called temporary hardness, where as hardness due to chlorides and sulphates ofCa, Mg and other compounds is known as non-carbonate hardness or permanent hardness. If noBarium and Strontium salts are dissolved in the water the sum of temporary and permanent hardnessgives the total hardness. Typical impurities in raw water is given in table 1:

Table 1

Cationic Anionic Nonionic Gases

Minerals Alkalinity due to

Ca++ Bicarbonate Turbidity CO2

Mg++ Carbonate and silt/mud H2S

Na++ Hydroxide dirt colour O2

K++ SO4= organic matter Chlorine

NH4+ Cl– colloidal silica NH3

Fe++ Nitrate Micro organism and

Mn++ SiO2 Bacteria, Oil

Organic matter algae, suspended

colour vegetation

WATER TREATMENT

13Chapter

111

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112 REFERENCE BOOK ON CHEMICAL ENGINEERING

For converting to equivalent CaCO3 divide the Fig. for ions by its equivalent wt. of ions andthen multiply by 50 (e.g., wt. of CaCO3)

Example : (i) for 40 ppm as Ca++ ion conc., equivalent CaCO3

= 405020

100× = ppm as CaCO3

(ii ) 40 ppm Ca as Ca++, divided by 20 to obtain 2 meq/lit

(meq = millieqivalent) calcium expressed as meq.

2.1 pH ValueIt is hydrogen ion concentration index and indicates whether a water sample is acidic, neutral

or alkaline (basic) and how many litres, as a power 10, of a soln. contain 1 gm of hydrogen ion.pH value of neutral water is 7 i.e., 107 lit of water contain 1 gm ion (1.008 gm) of Hydrogen ion.The total of pH and pOH values at 23°C are always 14.

pH = 7 neutral reaction (pH and pOH conc. are same)

pH < 7 acid reaction

pH > 7 alkaline or basic reaction

pH value is temperature dependent and for neutral pure water its values are :

Water temp°C pH value0 7.4923 7.050 6.63100 6.13200 5.69300 5.59370 5.63

3. ALKALINITYAlkalinity denotes the presence of bicarbonate of calcium, sodium, magnesium and iron, that

of soda ash (Na2CO3), potassium carbonate (K2CO3) or hydroxides (NaOH or KOH or NH4OH,hydrazine (N2H2) and other substances. It is measured by determining p and m values by titrationof water; p value is given by (use of phenolphthalein indicator) on a 100 c.c. water sample treatedwith the quantity in c.c. of 0.1 N HCl at colour change and as of m value is obtained from thequantity in c.c. of 0.1 N HCL using methyl orange indicator at colour change. This is given in T2.

4. DETAILED PROFORMADetailed analysis of water, for ascertaining treatment method for process/boiler/potability, is

required to be carried out. Following detailed analysis are required for this purpose.

PhysicalColour temperature index – APHA unit

Turbidity – Jackson or APHA unit

pH

Conductivity – µs/cm

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WATER TREATMENT 113

Table 2Alkalinity of water as mg CaCO 3/l

Water containsTitration result, ml/c.c Bicarbonates Carbonates Hydroxides

p = 0, M > 0 M nil nil

p < ½ M (2p < M) M – 2p 2p nil

p = ½M (2p = M) nil 2p nil

p > ½M (2p > M) nil 2(M–p) 2p–m

p = M nil nil M

Note: p and M in ml/c.c.

Physical (contd.)Total suspended solids, mg/lit and size range, mm

Hardness : Ca hardness as CaCO3 mg/l

Mg hardness

Temporary hardness as CaCO3, mg/lit

Permanent hardness

Total hardness

Non-carbonate hardness, as CaCO3, mg/lit

Carbonate hardness, as CaCO3, mg/lit

Nitrous nitrogen

Nitrate nitrogen as N, mg/lit

Ammoniacal nitrogen

Alkalinity – in p value or M value as CaCO3 mg/lit

Total dissolved solids, mg/lit

Permanaganate value

(4 hrs at 26.6°C)

C.O.D (Chemical Oxygen Demand), mg/lit

Sulphates as CaCO3 mg/lit

Chlorides as CaCO3 mg/lit

Fluorides as CaCO3 mg/lit

Post chlorination, Cl2 content in water.

MineralsSodium as Na mg/lit

Magnesium as Mg mg/lit

Iron as Fe mg/lit

Copper as Cu mg/lit

O

Q

PPP

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114 REFERENCE BOOK ON CHEMICAL ENGINEERING

Zinc as Zn mg/lit

Arsenic as As mg/lit

Lead as Pb mg/lit

Bacteriological

B.O.D5, mg/lit

(5 days at 20°C)

Total colliform as M P N/100 ml

Fecal coliform as M P N/100 ml

Note. Permanganate value gives the organic matter present in water, which is also removed bychlorination.

Raw water having high BOD value, (over 4–6), total/MPN colliform, (10,000), fecal colliformmore than 200, higher pH (over 10), chlorides (over 600), fluorides (over 1.5), along with arsenic,lead and zinc are not desirable for chemical treatment and to be rejected. Turbidity above 14,000 ppmis also difficult to remove and requires presettling ponds.

5. WATER SOFTENINGA. Chemical Treatment

(i) For removing temporary hardness due to presence of bicarbonates of calcium and magnesium,quicklime, CaO or slaked lime (hydrated lime), Ca(OH)2 is used in calculated quantities with excessamount due to impurity. The bicarbonates react with lime (or its solution, milk of lime).

Ca(HCO3)2 + Ca(OH)2 = 2CaCO3 + 2H2O

Mg(HCO3)2 + Ca(OH)2 = MgCO3 + CaCO3 + 2H2O

2NaHCO3 + Ca(OH)2 = CaCO3 + Na2CO3 + 2H2O

CO2 + Ca(OH)2 = CaCO3 + H2O

(ii ) Quantity of quick lime required for softening

If A is the temporary hardness due to calcium and B is due to magnesium expressed inequivalent CaCO3 in mg/lit unit, then pure quick lime required for above reactions is (A+B) × 0.74gm per m3 of raw water.

The purity of quicklime is considered to arrive at actual quantity required. Addl. quantity ofquick lime is required if alkalinity due to NaHCO3, is present. Mg alkalinity removal by slaked limedosing, the following reaction is also possible:

Mg(HCO3)2 + 2Ca(OH)2 = Mg(OH)2 + 2CaCO3 + 2H2O

In the above case pure quicklime required is 0.765 gm pre m3 of raw water for each mg forMg hardness as CaCO3 (mg/lit). Temporary hardness is removed by boiling when insoluble CaCO3or MgCO3 precipitates:

heat3 2 3 2 2Ca( CO ) CaCO + CO + H OΗ →

heat3 2 3 2 2Mg( CO ) MgCO + CO + H OΗ →

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WATER TREATMENT 115

(iii ) Permanent hardness is determined by difference between total hardness and temporaryhardness. Permanent hardness in water is due to presence of sulphates, chlorides and nitrates ofcalcium and magnasium. It is removed by dosing soda ash along with slaked lime. Dual use of slakedlime and sodium carbonate is useful to remove sulphates and chlorides of magnesium.

CaSO + Na CO CaCO + Na SO4 2 3 3 2 4 →

MgCl + Na CO + Ca(OH) Mg(OH) + CaCO + 2NaCl2 2 3 2 2 3 →

MgCl + Na CO MgCO + 2NaCl2 2 3 3 →

4 2 2 3 2 3 2MgSO + Ca(OH) + Na CO Mg(OH) + CaCO + 2Na S→

Ca(NO Na CO CaCO NaNO3 2 3 3 3)2 2+ → +

Calcium bicarbonate also reacts with soda ash:

3 2 2 3 3 3Ca(HCO ) Na CO CaCO 2NaHCO+ → +

(iv) Quantity of pure sodium carbonate required if C is the permanent hardness due to sulphates,chlorides and nitrates of Ca, Mg expressed as equivalent CaCO3 in mg/lit = C × 1.06 gms per m3

of water.

B. Sedimentation of Precipitates from Chemical DosingFerric alum containing Aluminium sulphate and ferric sulphate is used as coagulating agent in

the clarification of water, which hastens sedimentation process of reaction products from reactionof slaked lime and sodium carbonate. In the flocculation chamber of the clarifier, floc. formationoccurs in presence of coagulating agent, ferric aluminium. Aluminium sulphate completely hydrolysesin water to form insoluble aluminium hydroxide, which is colloidal in nature having negative charge.

Al (SO H O Al(OH) H SO2 4 2 3 2 4)3 6 2 3+ → +

The precipitates from dosing reactions as above bear positive charge which attract jelly likeprecipitate of Al(OH)3 to form bigger particles which settle in the clarification zone of clarifier alongwith sediments present in the raw water.

Part of aluminium sulphate reacts with the calcium and magnasium in water forming Al.Carbonate which immediately hydrolyses to Al(OH)3.

Al2(SO4)3 + 3CaCO3 = Al2(CO3)3 + 3CaSO4Al2(CO3)3 + 6H2O = 2Al(OH)3 + 3H2CO3

The alum floc produced by coagulation being much heavier settles to the bottom of clarifierfrom which it is periodically removed during blow down.

Calcium precipitate sludge, sp. gr. = 1.2 settles at 3 times faster than alum floc.

Al(OH)3 floc is formed according to alkalinity present in water after chemical dosing.

Normal alum dose required = 5 – 10 mg/lit. The min. dose is 5 mg/lit. Extent of alum doserequired is determined by jar test.

Quality of treated water: In lime soda process, total alkalinity must exceed the residual totalhardness. Carbonate alkalinity must exceed magnesium and Ca hardness. Caustic alkalinity can beincreased by increase of lime feed and carbonate alkalinity by increasing soda feed.

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Table 3Settling velocity of particles in water

Settling velocity, m/sec

Diameter of Sand Alum flocparticles Sp. gr. 2.65 Sp. gr. 1.05

mm at 20°C at 20°C

1 12 0.1

0.5 7.8 –

0.1 1.04 –

0.05 0.2 –

0.01 0.013 –

New poly electrolytes have been developed as a coagulant in mid 70’s. Though its cost is muchmore than ferric alum, but quantity required is less (dose = 0.1 mg/lit or 0.1 gm/m3). It can be usedwith min. alum dose and put into intake channel to flocculator after alum is added and flocculationis started.

C. Lime Softening Process by ClariflocculatorUsually a sludge blanket type of flocculator is used for water softening. Required quantities of

lime and alum solutions were prepared based on raw water analysis and mixed with water in flashchamber from where it is sent to central flocculator section of clarifier. This section is provided withfour paddle agitators rotating in opposite directions. Here, chemical reactions between bicarbonatesof Ca and Mg and milk of lime take place and carbonates of these salts precipitate out. Theprecipitated carbonates form flocks with Al hydroxide, formed due to hydrolysis of alum becomebigger and flows to outer clarification section. The heavier flocks settle to the bottom conical portionwhere the sludge blanket is formed which do not allow any flocks to leave the clarifier clear watertrickles from holes in top periphery of clarifier and is stored in storage tank.

The bottom scraper, which moves very slowly scrapes the heavy sludge, swept in towardscentral sludge water discharge valve and the valve is opened usually once in a shift for sludge drain.The success of this process depends on proper floc. formation, which depends on alkalinity presentin water after dosing of chemicals. Total sludge formation is 2.8 – 3.6 times the wt. of lime added.The treated water is then subjected to sand gravity filtration to remove any carry over smalls offlocks/suspended matter. Then chlorination is done in pump discharge line from filtered water storagetank. Chlorination from large cylinder is usually done through dosing instrument. Often pre-chlorinationis required if organic matter is high.

Removal of Iron and Manganese Salts in WaterBoth iron and manganese salt can be removed by aeration. Ferrous salts get oxidized to ferric

state and precipitated out:

4 42Fe(HCO O H O Fe(OH) + 8CO3 2 2 3 2) + + →

4 10 44FeSO O H O Fe(OH) + 2H SO2 2 3 2 4+ + →

In case of high carbonate hardness, the liberated sulphuric acid is decomposed as below:

H SO Mg(HCO ) MgSO + 2H O + 2CO2 3 2 4 2 24 + →

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WATER TREATMENT 117

River Water

Coarse travellingscreening

River water pumps

River water storage

Fire travelling screening

Acration(if needed)

Prechlorination

Chemical m ixingand coagulantaddition

Clarifier(F locculator)

Gravity filters

Process waterstorage

PH correction andPost chlorination

Water forProcess use

Water to D.M . plant forboiler use

Sanitary water

From chem ical Section

Wash Water

Wash Water

Sludge

Clear

Water recycleSludge

Treatment

Slu

rry

to r

iver

dis

char

ge

River Water Treatm ent Schem e

Fig. 1. Block diagram for river water treatment scheme.

In case where carbonate hardness is minor, addition of milk of lime is required to precipitateiron, Fe(OH)2 and the hydroxide is oxidized during aeration:

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118 REFERENCE BOOK ON CHEMICAL ENGINEERING

4 2FeSO Ca(OH)+ 2 4Fe(OH) + CaSO→

2 2 24Fe(OH) O 2H O+ + 34Fe(OH)→Manganese is converted into manganese dioxide by aeration:

3 2 2 22Mn(HCO ) + O + 2H O 2 2 2 2MnO + 4H O + 4CO→

4 2 22MnSO + O + 2H O 2 2 4 2MnO + 2H SO→If carbonate hardness is high, liberated H2SO4 decomposes the carbonate as above. Otherwise

alkalinity raising agents like milk of lime is to be used. The insoluble compounds of iron andMagnesium precipitated as above can be removed by gravity filters.

Quantity of air required for oxidation by aeration:

1 mg Fe/lit = 1 lit air/m3 water

1 mg Mn/lit = 2 lit air/m3 water

Example. For 0.2% Fe or 0.2 × 104 = 2000 ppm Fe, air required = 1 × 2000 lit/m3 or 2m/m3 of water aerated.

If quantity of water thus treated is 300 m3/hr, air flow required for aeration = 2 × 300 or 600m3/hr.

Note : If water contains a little O2, addln. 28 lit of air/m3 of water are to be added to formlime anti corrosive layer to maintain pH at above 6.5.

Removal of ferrous and manganaous ions by sodium hydrogen cation exchangers is possibleif no dissolved air or oxygen is present.

E. Demineralisation by Ion Exchange MethodHigh quality water required for boilers and other process use, is further treated in ion exchangers

in chemical plants and power generation plants for boiler use.

Process water from water treatment plant after chemical dosing, flocculation and sedimentationin a clarifier is further treated in demineralisation plant consisting of degassifier, pressure filter andfor removal of dissolved oxygen and carbon dioxide and finally treated in cation, anion and mixedbed exchangers. Additional pressure filter is required in DM plant to arrest any suspended matterfrom process water treatment plant.

Filtration by pr. Sand filters is carried out in filters packed with gravel (non crystalline structureat bottom and sand layer at top). Water at 2–3 Kg/cm2 pr. is fed at the top and during its downwordsflow, fine suspended matter is arrested in sand bed and clear water is drawn from the bottom. Twofilters are required–one remains in line and other one under back washing to remove the trappedsuspended water. Depending on the capacity of DM plant, a battery of such filters is required.

F. Degasification of Water

(i) Thermal degasification of water removes dissolved gases (O2 and CO2) using live steam indegasification tower having contact plates. The water temperature is brought to near its boiling point.the solubility of O2 and CO2 is reduced due to heat as well as partial pressures are reduced to zero.Thermal degasification is either carried out under vacuum through a vacuum pump or a condensercum ejector for exhausting liberated gases and excess steam are released from tower top. Whencondenser is used inlet feed water to degasifier is preheated in the condenser for heat recovery beforeit is fed to the tower from top through distributors. Pressure degasification is used mostly in power

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WATER TREATMENT 119

plants using steam pressure controllers for uniform degasification temperature. In vacuum degasification,temperature controllers are used for this purpose.

(ii ) Chemical degasification of water is usually carried out after demineralization of water bydosing N2H4, as hydrazine hydrate (purity 75% min.) to remove residual dissolved oxygen. Themineral content of water is not increased and excess hydrazine is decomposed due to heat in boilers.NH3 gets mixed with steam and is condensed as condensate where as N2 remains with steam andis removed as non-condensable gases from process condensers. Hydrazine concentration required fora typical DM plant is 2–5 ppm; the reactions are:

2 4 2N H + O 2 2 2H O + N→

2 43N H 3 2 4NH + N→

G. Ion Exchangers for DM waterBoilers, specially medium and high pressure boilers, require feed water of zero hardness and

free from silica. Cation exchangers, filled with suitable resins to remove all +ve ions like Ca, Mg etc.and anion exchangers are filled with required resin for the removal of –ve ions groups including silica.Ion exchangers contain fine granules of organic substances, which are styrene based syntheticresins. Cation exchanger contains strong or weak acid groups and anion exchangers contain eitherstrong or weak basic groups. Cation exchangers are regenerated after exhaust on suitable period ofexchange of +ve ions in water by either dil. H2SO4 or HCl (5–10%) as per requirement. Similarlyanion exchanger are regenerated after exhuast by weak caustic soda solution (3–5%). After exhaustionof cation and anion exchanger, backwash with water is carried out to remove suspended matterfollowed by regeneration with acid/alkali. First rinsing with water, removes excess regenerationchemicals and exchangers, thus regenerated, are put in line. All these operations are controlled bytimer operated control valves. Normally 1 + 1 cation exchanger and 1 + 1 anion exchanger arerequired for 1 exchanger is in operation and l as stand by after regeneration.

Selection of Type Cation and Anion Exchangers ResinDepending on the extent of hardness (temporary/permanent or carbonate hardness or non

carbonate hardness or Ca/Mg hardness) present in treated process water or underground water,suitable type of ion exchange resins is to be selected. For medium and high pressure boiler, instantaneousremoval of silica is required in mixed bed exchanger containing both cation and anion exchange resin.Cation exchanger (H exchange) removes alkalinity and hardness. The weak cation exchanger ischarged with H ions. All the mineral content in water is reduced by the amount of carbonatehardness.

Decarbonation (H exchange)

Ca Ca

Mg.(HCO3)2 + A.H2 → 2H2O + 2CO2 + A.Mg Na2 Na2

Regeneration:

Ca Ca

A.Mg + HCl → AH2 + MgCl2Na2 Na2

Obtainable value : < 0.5 mval/lit

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120 REFERENCE BOOK ON CHEMICAL ENGINEERING

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WATER TREATMENT 121

Quality of acid required per m3 of decarbonated water is 14 gm 100% HCl/°dH carbonatehardness (German hardness unit).

Debasification (H exchange)A strongly acid cation exchanger is used which is charged with H ions. All the cations contained

in water are exchanged for H ions. The resulting water contains acids corresponding the anions. Ca Ca

Mg.(HCO3)2 + A.H2 → 2H2CO3 + 2H2CO3 + A.Mg Na2 Na2 Ca Ca

Mg.SO4 + A.H2 → H2SO4 + A.Mg Na2 Na2 Ca Ca

Mg.Cl2 + A.H2 → 2HCl + A.Mg Na2 Na2

Regeneration Ca Ca

AMg + 2HCl → A.H2 + Mg.Cl2 Na2 Na2

Quantity of acid required per m3 of debasified water is 32 gm 100% HCl/°dH cation hardness.A.H2 stands for cation exchanger resin.

Anion Exchanger Resin (OH Exchange)Strongly and weakly basic anion exchanger resins are used which are charged with OH ions.

This type of resins removes acidity from water.

DeacidificationStrongly basic exchanger resin;

2 3 2 2 3

2 3 2 2 3

H CO A.(OH) 2H O + A.CO

H SiO A.(OH) 2H O + A.SiO

+ →

+ →

Weakly basic exchanger resin:

2 2 2

2 4 2 2 4

2HCl A.(OH) 2H O + A.Cl

H SO A.(OH) 2H O + A.SO

+ →

+ →Regeneration with dilute NaOH solution.

3 2 2 3A.CO 2NaOH A.(OH) + Na CO + →

3 2 2 3A.SiO 2NaOH A.(OH) + Na SiO + →

2 2A.Cl 2NaOH A.(OH) + 2NaCl+ →

4 2 2 4A.SO 2NaOH A.(OH) + Na SO+ →N. B: A (OH)2 stands for anion exchanger resin.Quantity of dilute NaOH solution per m3 of deacidified water;(i) Strongly basic, 40–60 gm NaOH 100%/°dH anion hardness.(ii ) Weakly basic, 18–22 gm NaOH 100%/°dH anion hardness.

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122 REFERENCE BOOK ON CHEMICAL ENGINEERING

(b) In case of total demineralization with removal of silica, the above scheme of resin usageis slightly modified for deleting basic anion exchange resin and entirely strongly basic anion exchangeresin is used which ensures removal of SlO2 and CO2. Often due to initial CO2 content of inlet waterto DM plant, after degasser, is produced in cation exchanger from carbonate hardness; CO2 the sizeof anion exchanger can be reduced and regenerating chemical requirement decreased by installing aCO2 scrubber using air (counter current flow) to bring down CO2 content to 10 ppm (10 mg/lit).Alternatively a mixed bed exchanger after anion exchanger contains both strongly acid cation exchangeresin and strongly basic anion exchange resin. Mixed bed exchangers are however, always used intotal demineralisation plant and a recycle condensate polishing unit (cation exchanger) is required.The conductivity of DM water, after mixed bed in a total demineralisation plant, should be below 0.5µs/cm and the residual silica should be maximum 0.05 mg/lit (0.05 ppm). For super-critical boilersilica content should be about 0.01 ppm.

(c) DecarbonisatonWhen only carbonate hardness is required to be removed, cation exchanger is filled with weakly

acid exchanger resin. The hydrogen carbonate cations are exchanged for H ions. Hardness of saltsimparting non-carbonate hardness and neutral salt remain in water. The mineral content of water isreduced by the amount of carbonate hardness.

(d) Neutral Exchanger Resin (Na Exchange)Here all Ca and Mg ions are exchanged for Na ions and thus removed. The minerals content

of the water remain unchanged.

Ca CaMg.(HCO3)2 + A.Na2 → 2NaHCO3 + A.Mg

Ca CaMgSO4 + A.Na2 → Na2SO4 + A.Mg

Ca CaMgCl2 + A.Na2 → 2NaCl + A.Mg

Regeneration is by dilute sodium chloride soln.

A.Ca + 2NaCl → A.Na2 + CaCl2 Mg Mg

Possible hardness obtainable depending on composition of feed water is <1.8 mg CaCO3/lit.

(e) Partial DemineralisationTwo strongly acid cation exchangers, connected in parallel – one in Na form and the other in

H – exchange form, are used. The Na exchange resin removes all Ca and Mg ions for Na ions andNaHCO3 from Na exchanger is decomposed by the acid in H exchanger. The mineral content ofthe water is reduced by the amount of carbonate hardness. Regeneration is by HCl & NaCl solutionsrespectively.

(i) Series connection of exchanger. Weakly acid cation exchanger in the H form followed bystrongly acid cation exchanger in Na form, the CO2 liberated from carbonate hardness can beremoved by degassing after Na exchanger. Water quality is same as that of partial flow method.Regeneration is by HCl and NaOH respectively.

(ii ) Mixed bed exchanger. A single cation exchanger containing both weakly acid and astrongly acid exchange resins can be used also. The quality of water is equal to that for parallel flow

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WATER TREATMENT 123

method. Regeneration is 1st by dilute HCl and then by NaOH. This method is suitable for water whennon-carbonate hardness comprises 20–40% of total hardness.

(f) Condensate PolishingFor recycle of steam condensate with tolerable limits of impurities, cation exchanger, containing

strong hydrogen resin, is used. Here NH4+ ion in condensate upto a certain limit can be used.

Regeneration is by dilute acid, H2SO4 or HCl.

(g) ZeolitesInitially Na2 zeolite, a cation exchanger was developed for removal of hardness in water.

Chemically zeolite is sodium salt of aluminium orthosilicate.

Na2(Al2Si2O8) + CaCl2 → Ca(Al2Si2O8) + 2NaCl

After exhaustion it is regenerated with 10% NaCl soln.

Ca(Al2Si2O8) + 2NaCl → Na2(Al 2Si2O8) + CaCl2

6. DESALINOTION OF SEA WATER:The process is based on reverse osmosis. In case of osmosis, water moves through a semi-

permeable membrane from a low conc. to high conc. of solute due to pressure difference causedby solute as per Henry’s law. The osmotic pressure is the pressure required to stop the flow ofsolvent through the semipermeable membrane.

In case of reverse osmosis, the barrier membrane is usually called semipermeable which isselective so that solvent can only pass through the membrane while the solute can not pass throughthe membrane. This property of the semi-permeable membrane is used in osmotic pressure filtrations.In order to separate water from dissolved solids by reverse osmosis, the applied pressure of water,containing dissolved solids, must be greater than osmotic pressure.

The principle of separation of salt (NaCl) from sea-water by reverse osmosis can be calculatedfrom the following equation;

1 FW = A.(∆P-∆π)

Where, FW = water flux through the cell, gpd/ft2 (Us gallon per day/ft2)

A = water transport co-eff, gpd/ft atmosphere

∆P = pressure difference applied across membrane, atmosphere

∆π = osmotic pressure difference across semi-permeable membrane, atmosphere

The solute flow is given by equation:

2. F S = B. ∆C

Where, FS = salt flux, gpd/ft2

B = salt transport co-efficient

∆C = C1 – C2

C1, C2 = conc. of solute at upstream & down stream of membrane respectively, lb/ft2

Sea water purification plant usually contains, sea water pumping system, filters. Reverseosmosis battery of cells, desalted water tanks and finally vacuum distillers. Usually some salt is addedto desalted water to impart test to water.

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124 REFERENCE BOOK ON CHEMICAL ENGINEERING

The most critical part of the purification plant is semi-permeable membrane. Usually syntheticpoly amide (nylon fibers) is used for desalination of sea-water. For other reverse osmosis processnatural cellulose acetate or nitrate is used where feed water to cells must be acidic to preventhydrolysis of membrane.

Sea water desalination is suitable where fresh water source is scarce for potable water but thecost factor is quite high. In middle east, such plants in higher capacity range are quite common.

Water Treatment by Magnetic FiltrationRaw water can be treated for separations of suspended & dissolved solids by magnetic filtration

method.

Separation method;

This resorts to magnetic seeding first and then flocculation process separates diamagneticsuspended solids and dissolved solids.

The paramagnetic suspended solids present in fluids, minerals and pharma items as well as oilshave no magnetic seeding requirement. for separation.

Selection of magnetic filtration depends on various factors viz;

(i) Size of feed materials in water.

(ii ) Relative magnetic response.

(iii ) Purity requirement of treated water, feed water temperature and point of feed.

(iv) Permanganate strength.

(v) Type of feed-liquid, wet and dry.

(vi) Operating cost.

Process: Seeding of raw water with grounded Ferro magnetic particles, is done followed byverification. Finally the water is passed through a narrow constriction in a permanent magnet whereremaining impurities are attracted and clear water is obtained.

The principal of magnetic filtration is also used for separation of Ferro magnetic particles/pieces from ore trailing, coal & coal-washery where the above moving materials are caught usingpermanent magnet hung over the conveyor.

Ionic LoadTo convert load of a water sample to their ionic equivalent, no. of ions must be divided by its

equivalent wt. of ions. Exm. : to convert Ca+ + = 40 ppm, dividing by equivalent wt., ( )Atomic wt.

=20,valency

we get 2 meq of calcium.

Bacteriological contamination in raw waterSurface water often contains high micro-organisms due to contaminations with human excretion,

untreated waste from municipalities, rain water pouring into rivers/lakes etc. Under ground water isusually free from bacteriological contamination but contains organic matter.

Quality of raw water

Item Acceptable source

Avg. B. O. D 0.75 – 1.5 mg/lit

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WATER TREATMENT 125

(5 days, 30°C)

Maxm. B. O. D. 1–3 mg/lit

Avg. Colliform, MPN 0/100 ml

Maxm, Colliform 0/100 ml

pH 6 – 8.5

Chlorides < 150 mg/lit

Fluorides < 1.5 mg/lit

Arsenic 0.01 mg/lit (max)

Pb ≤ 0.1 ppm

Chromium +6 ≤ 0.05 ppm

Copper ≤ 3 ppm

Iron & Mn ≤ 0.3 ppm

Zn < 15 ppm

N.B MPN stand for most probable number

Typical analysis of safe bottled drinking water: as per IS-14543-98 as amended 2003

pH = 6.5–8.5 Mercury as Hg = ppm 0.001, max

Colour = 2, max Copper as Cu = ppm 0.05, max

Cl– as Cl = ppm 200 max Manganese as Mn = ppm 0.1, max

SO4= as SO4 = ppm 200, max Zinc as Zn = ppm 5, max

NO3- as NO3 = ppm 45, max Aluminium as Al = ppm 0.03, max

F- as F = ppm 1.0, max Lead as Pb = ppm 0.01, max

HCO3– = ppm 200, max Cromium as Cr = ppm 0.05, max

Alkalinity Nickel as Ni = ppm 0.02, max

Minerals Selenium as Se = ppm 0.01, max

Na+ as Na = ppm 200, max Cadmium as Cd = ppm 0.01, max

K+ as K = ppm - Barium as Ba = ppm 1.0, max

Ca+ + as Ca = ppm 75, max Phenolic compounds = ppm 0.001, max

Mg+ + as Mg = ppm 30, max (as C6 H5 OH)

Fe+ + + as Fe = ppm 0.1, max Arsenic as As = ppm 0.01, max

Colliform = nil Mineral oils = 0.01 ppm

TDS = ppm 500, max Anionic s. active

E. Coli, SRB etc. – absent agent as MBAS = ppm 0.2, max

Turbidity = N TU 2, max PCB = Not detectable

B. O. D5 = nil Polynuclear aromatic = No

Odour = agreeable hydrocarbons = detectable

Total pesticide residue =0.5 µgm/1 Free chlorine = ppm 0.2, max

Single pesticide = 0.1 µgm/1 Taste = agreeable, NO2 = 0.02 ppm (max)

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126 REFERENCE BOOK ON CHEMICAL ENGINEERING

Arsenic Removal ProcessThere are several arsenic removal processes:

Process Range of removal

(i) Lime softening 0.2 to 0.03 mg/lit as As

(ii ) Charcoal filtration 0.2 to 0.06 mg/lit as As

(iii ) Ferric sulphide filter hydroxide 0.8 to 0.05 mg/lit as As

(iv) Co-agulation with ferric hydroxide 25 to 5 mg/lit as As

(v) Precipitation with ferric hydroxide removed upto 0.6 mg/lit as As

(vi) Micro filtration semi-permeable membrane < 0.8 mg/lit

Micro filtration removes pesticides to allowable limit as per EN standard, EN 29000. Arsenicfrom arsenic bearing rocks is leached in underground waterstrata which when pumped out by tubewells for drinking purpose cause the arsenic poisoning in humans and animals.

Chlorination of Water for Disinfection(i) By direct injection of Cl2 from Cl2 cylinder.

(ii ) By bleaching powder spreading in sand/gravel filter.

(iii ) By electrolytic chlorinator.

Residual Cl2 in drinking water = 0.2 ppm

Effect of Cl2 : kills bacteria, removes bad odour, reduces BOD & decolourisation.

Water Treatment Basic1. Turbidity – Due to presence of various sediments viz dirt, mud, clay etc. turbidity of surface

water increase in raw water. If turbidity exceeds 14000- mg/1 pre-settlement pond is necessarybefore the water treatment plant, which removes 70% turbidity. Turbidity measured byJackson meter or APHA. After settling pond 2.5 – 5 JTU water preferred.

2. Non carbonate hardness – Due to sulphates and nitrates, soda ash removes them.

3. Algae – For prevention of greenish algae growth a 0.3% CUSO4, 5H2O soln is suitable whichacts as a biocide.

4. 1 mg/lit alum will react with 0.45 mg/lit alkalinity expressed as CaCO3 or 0.28 mg/lit limeas CaO or 0.35 mg/lit slaked lime, Ca(OH)2 or 0.48 mg/lit Na2CO3.

5. The floc formation reaction is reversible and its formation is favorable at pH 6.8 – 7.9.

6. Presence of nitrates and nitrites may be due to decomposition of organic wastes.

7. Above 600 ppm chlorides, a salty taste is developed.

8. Fluorides > 1.5 mg/lit (as F) is undesirable as it can cause mottling of teeth at 3 ppm andabove.

9. Sand gravity filter, filtration rate is 1 m3/m2/min for a bed size of 1.15 m2 and bed depth30–45 cm of gravel below 60–75 cm sand. Period in between backwash 24–72 hrs andwater required = 6% of filtered water.

10. Water is classified as hard if it is containing more than 120 mg of divalent ions (Ca & Mg)per lit ( 454 mg/lit) usually expressed as CaCO3.

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WATER TREATMENT 127

11. Sodium cycle ion exchange increases the soluble solids content as 2 sodium (2×23 = 46)are substituted for one calcium (40) or one magnesium (24.3).

12. Hydrogen cycle exchanger replaces 1 calcium or 1 magnesium with 2 hydrogen and thisreduces the total solids but also reduces the pH.

13. In odour scale potable water should be less than 3.

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128 REFERENCE BOOK ON CHEMICAL ENGINEERING

14METAL CLEANING PROCESS

Chapter

A. METAL DEGREASING(a) Chemical cleaning is done by trichlorethylene or percholorethylene. Special Vat is required

with heating coils at bottom & cooling coils at top to reduce loss of chemicals due to heating duringdegreasing operation. The soiled articles are dipped in the vat and heated for 10–20 minutes.

For heavily greased articles, often dipping in boiling solvent may be required. Degree ofcleanliness test is done by observing wetability, as shown in breaks or spray pattern test.

(b) Alternate to chemical degreasing by the above organic solvent, hot alkaline soln. dipping.is also done. It is a mix of sodium hydroxide, silicates and phosphates. The soln. saponifies oils andorganic materials. The pH range of such soln. for steel is mildly alkaline or it is neutral for aluminium& zinc alloys.

B. ACID PICKLING FOR REMOVING SCALES ON METALS(i) Iron & steel – dilute HCl for minor scale

– hot dilute H2SO4 for thicker scales

(ii ) S.S – dilute HNO3

(iii ) Al alloys – dilute HF

(iv) Cu and its alloys –hot dilute H2SO4

(v) Brass – mix of H2SO4, HNO3 and little NaCl or Na2Cr2O7 & H2SO4.

C. CLEANING STEEL TUBES/PIPES FOR COMPRESSORS/PUMPS LUBE OIL CIRCUIT AND REFRIGERATION PIPE LINES

(i) For smaller dia tubes. Dilute HCl (5–6%) is generally used at temperature of 30–40°C withcirculation. Circulation is to be maintained at least for 30 hours or more depending on rust condition.Dilute H2SO4 (5–6%) could be used for thicker scale deposits. Heating is done by L.P steam. Thisis followed by water wash, 2–3% alkali wash and again water wash.

(ii ) Dipping process. For large dia steel pipes for refrigeration pipe lines, dipping in 5 – 6%HCl or H2SO4 could be used. The after treatment with water wash, alkali wash & water wash hasto be followed.

(iii ) For S.S pipes/tubes use 5–6% dilute HNO3.

128

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METAL CLEANING PROCESS 129

D. ELECTROCLEANING OR CATHODIC CLEANING:Here the non ferrous items, to be cleaned, form the cathode in water containing electroplating

bath where H2 gas scours the cathode as it evolves at cathode. Anode is made of carbon rod. Thedisadvantage is that the cathode, thus cleaned, leaves the cathode surface passive due to H2 pick up.An additional dilute HCl dip is required for the cathodic articles after electrocleaning.

Anodic cleaning is desirable for soiled ferrous materials since volume of H2 at cathode is twicethe volume of oxygen at anode. The articles to be cleaned form the anode in an electrolytic bathcontaining water.

The electrocleaning D.C voltage is to suitably determined.

E. CATHODE COATINGHere the protecting materials are situated below the protected in the e.m.f series of metals.

Example- Tin plated iron. Tin, the protecting metal is placed below iron or steel in the e.m.f orgalvanic series.

F. ANODE COATINGHere the protecting material lies above the protected. Example- Nickel plated copper; Nickel,

being the protecting metal lies above copper in e.m.f series.

G. ELECTRO DEPOSITIONResins are coated on parts forming anode while resins form the electrolyte - cathode is made

of carbon rod.

H. ANODISINGAl articles form the anode and cathode is SS or carbon rod. Oxygen liberated at anode form

an oxide coating & colour is imparted on the anodized surface from the colour put in bath. The D.Cvoltages of the electrolytic bath varies for different electro cleaning or coating processes viz.

Cathode cleaning

Anodic cleaning

Cathode coating

(Tin plating on iron)

Anode coating

(Nickel plated copper)

Resin electro deposition

Anodising

Page 141: Reference Book on Chemical Engineering v. 1

There are three types of manganese dioxides of industrial importance.

A. SPEC. OF ACTIVATED MANGANESE DIOXIDEMnO2 = 90% wt primarily grade

H2O = 2% wt

Others = 8% wt mainly lower manganous oxides. Other critical impurities viz Cobalt, Nickel,Copper & Molybdenum and conc. are limited to 0.001%.

Particle Size80% < 44 µm for Leclanche cell

85% < 44 µm for Zinc. Chloride battery

Activated Manganous Ore Process (Semi-synthetic)Manganese ore (Pyrolusite) containing 80% Mn is roasted at 600°C to get Manganic oxide,

Mn2O3 which is then reacted with hot sulphuric acid to get activated MnO2.

2MnO2 Roasting → Mn2O3 + 1/2 O2

Mn2O3 + H2SO4 Heat → MnO2 + MnSO4 + H2O

Activated MnO2

MnSO4 is separated by leaching with water and activated MnO2 is dried. Activated MnO2 islesser effective than chemical manganese dioxide (C M D).

B. CHEMICAL MnO 2

Sedemar process for CMD: process involves step by step purification of impurities in pyrolusite(MnO2) ore:

Pyrolusite ore → Crushing → Rotary mill drying Partial air

Grinding → Reduction with → Rotary cooler → MnOHeavy fuel oil H.T

→ Leaching with → Neutralisation → thickening with sludge removalH2SO4 Na2CO3

15MANGANESE DIOXIDE

Chapter

130

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→ Filtering drum → Carbonation with → Filtration in a drum filterfilter NH3 and CO2 to remove

Mn (11) carbonate

→ Drying → Roasting in shelf → Belt cooler → MnO2roaster at 320°C Tech. grade(MnO 1.85)

→ Oxidation reaction → washing → Filtration → Drying → CMDwith H2SO4 battery grade

(Y – MnO2)

Reactions

Reduction : MnO2 +Heavyfueloil burning

Withltd.Air [15 MnO2 + C15H24S2 + 7.5O2 →

15MnO + 15 CO2 + 10H2OA + 2H2S]

Leaching : MnO + H2SO4 → MnSO4 + H2O

Na2CO3

Neutralisation : Fe2O3 + 3H2O →Fe(OH)3B+ 3H+

for Fe2O3 precipitation

Carbonation: MnSO4 + NH3 + CO2 →MnCO3 + (NH4)2SO4 - by product

Roasting : MnCO3 Roasting

C320° MnO1.85 + CO2

Tech. Grade

H2SO4

Oxidation : Mn1.85 + 2NaClO3 → MnO2 + Cl2 + Na2SO4

(CMD)

C. ELECTROLYTIC MANGANESE DIOXIDE (EMD)Specification: MnO2 = 91% (wt) – Hexanal modification

MnSO4 = 1–3% – hexanal modification

Fe = 0.02%

H2O = 3–5%

Others = 0.001%

Balance =lower MnO2

Density = 4–4.3 gm/cc

Surface area = 40–50 m2/gm

Particles size = 74 µm (<200 mesh)

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132 REFERENCE BOOK ON CHEMICAL ENGINEERING

Manufacturing ProcessRhodochromite ore concentrate is leached with H2SO4. The acidic MnSO4 is purified by

oxidation with MnO2 and neutralized with lime to pH of 4–6 when heavy metal ions (Fe, Pb, Ni andCo), present in ore, precipitate. H2S is often used for complete precipitation of heavy metals assulphide. After filtration and bringing conc. (filtrate) to 75–160 gm/lit MnSO4 and H2SO4, 50–100gms/lit MnSO4 soln. is then electrolysed (bath). The cell consists of open steel tank lined withhypalon, rubber or ceramic. (electrically non conducting). The anode is made of graphite, Ti or hardlead. The cathode material is manganese.

The paraffin layer over electrolyte is used to reduce evaporation.

Electrolysis parameters :

Cell voltage = 2.2–3.0 v

Anode current density = 70–120 A/m2

Bath temperature = 90–98°C

Yield = 70–90%

EMD is deposited on anode. Cell operation is stopped when solid E M D thickness of about20 – 30 mm is obtained at anode in 15–20 days. During electrolysis, H2SO4 conc. is increased whileMnSO4 conc. is depleted. Hydrogen is liberated at cathode.

Cell Reaction

Anode : Mn+2 + 2H2O → MnO2 + 4H+ +2e

Cathode: 2H+ + 2e– → H2

Mn+2 + 2H2O → MnO2 + 2H+ H2

E M D after end of electrolysis is removed mechanically, crushed & thoroughly washed withhot D.M water, dried and finally grounded. The grinded product is again mixed with water and pHbrought to 6.5 – 7 with alkali, dried to specified moisture and packed.

Modern trend is to use Ti anodes and use of passivation retardants (finally grounded MnO2,Mn2O3 & Mn3O4) in electrolyte bath and use of current density over 150 A/m2.

Uses of Manganese Dioxides(i) Activated MnO2 is used as a depolariser in dry cell battery.

(ii ) Chemical MnO2 (CMD) is used in glass industry, drystuff and varnish. Catalysist, colouringof bricks and ceramics, welding rod manufacture, metrological products and also as a trace nutrientsfor plants.

(iii ) Electrolytic manganese dioxide (EMD) is mainly used in dry cells as a depolariser andferites manufacture for electronics use.

Page 144: Reference Book on Chemical Engineering v. 1

In high wind areas like sea coastal places, wind power is generated in wind turbine generators(WTG) which are usually two or three bladed; modern trend being to use two bladed WTG. Siteselection is through wind mapping of the proposed site for few years and other project relatedinfrastructure availability, including power evacuation through transmission lines of state electricityboard and power transmission grid.

Generally the wind turbine generator is located high at 30–50 meter above the ground level(to have access to more wind speed for AC power generator at the WTG, (3 phase AC generator).The AC power is converted to DC by a rectifier and stored in large Ni-Cd battery house and powerfrom battery is converted to AC 3 phase in inverter and transmitted to 3 phase AC transmission lineafter voltage boost up to grid voltage. The battery storage is used for low demand period. Nickel–Cadnium battery has higher cycles of operation, charge to discharge, about 2000)

The blade pitch could also be automatically adjusted to suit generation. In direct AC powertransmission, power is transmitted to step up transformer by passing rectifier battery-inverter systemor transmission to grid. A wind power generator farm requires a large area (5–6 acres/MW) as WTGare to be placed at specified distances. The center line distance between two adjacent WTG shouldbe 7 times the diameter of WTG blade circles and 2 blade circles center distances should beminimum 5 times the diameter of blade circles. The minimum wind speed required is 6 miles/hr (9.66km/hr) and maximum wind velocity allowable is 39 miles/hr (62.79 km/hr) with alternator cut offspeed kept at 40 miles/hr (64.4 km/hr) during storm. The WTG capacity usually varies from 25 KWto 100 KW and the minimum capacity of a wind power firm could be 250 watt and the annual powerproduction could be 600 thousand kilo watt-hr. The efficiency of power generation in WTG set isonly 35 to 60 percent. A constant speed WTG spills wind energy at higher wind velocity to allowgenerator not to exceed rated capacity upto certain limit during storm before cut-off device isactivated for which blade pitch auto adjustment device is put in two blade turbine.

Kinetic energy of wind, E = 1/2 ρu2 where u = wind velocity in m/sec and ρ = density of air.

For two bladed generators, equation for wind power is given below:

P/AT = 1/2 u3

Since only 8/27/1 2 or 16/27 or 0.593 part of maxm. power can be extracted, the effectiveequation for power:

WIND TURBINE FOR POWERGENERATION

Chapter

16

133

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134 REFERENCE BOOK ON CHEMICAL ENGINEERING

Fig. 1. 2 Bladed wind turbine power generator scheme (WTG).

PM/AT = 0.593. ρ.u.3 or PM = o.593.ρ.u.3π R2

Where PM = maximum power extracted

AT = cross section area of wind stream, sq mt. (blade sweep area)

0.593 = Betz co-eff maxm., fraction of power, which can be generated

ρ = Air density (sea level), 1.221 kg/m3 (usually)

u = Initial steady state wind velocity, m/sec

And power co-eff 3 2

P

1/ 2. . .c

u Rρ =

ρ πwhere P = power delivered to the turbine, kg-m/sec or watt

ρ = 1.221 kg/m3 density of air

u = initial wind velocity m/sec

R = radius of blade area, m

Power co-eff, is the ratio between power delivered to the turbine to the power extractedbetween the cross sectional area; usually power co-eff is 0.35 to 0.60.

Note. Power density for a 4.50 m/sec wind velocity is 54 W/m2 and the same for 13m/sec wind velocityis 150 W/m2. Power density is the power per unit cross section of wind stream.

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17CENTRIFUGAL PUMPS

Chapter

A centrifugal pump transfers the input mech. energy through a rotating impeller into kinetic(velocity) & potential (Pressure) energy to the liquid. This addition of energy will cause it to dowork, such as flow through a pipe or rise to a higher level.

While centrifugal force developed, depends both on the peripheral speed of the impeller and onthe density of fluid pumped, the amount of energy imparted to the fluid per lb of fluid is independentof the fluid itself i.e its density or sp. gravity so long the liquid viscosity is not higher than that ofwater. Pump head is expressed in feet of fluid generated by a centrifugal pump at a given speed andcapacity is usually expressed in m3/hr or cft/sec or GPM. In determining heads, it is required toconvert pressure expressed in Psi or Kg/cm2 into feet or meter of liquid.

CAPACITYThe volume of liquid pumped, is referred to as capacity and is generally measured in gallons

per minute (gpm). Large capacities are frequently rated in cubic feet per second, or millions ofgallons per day. When referring to the pumping of petroleum oils, the capacity is sometimes specifiedin barrels (42 US gal) per day.

HEADThe height to which liquid can be raised by a centrifugal pump is called head and is measured

in feet or meter of liquid. Water performance of centrifugal pumps is used as a standard ofcomparison because practically all-commercial testing of pumps is done with water.

System of heads: Head of a centrifugal pump is the energy content of the fluid expressed in ft lb/lb.

The total head of a system against which a pump must operate is made up of the followingcomponents.

(1) Static head.

(2) Pressure head.

(3) Friction head.

(4) Velocity head.

(5) Entrance and exit head losses.

135

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Static head. It is caused by the difference in elevation. Total static head is the difference inelevation between suction and discharge liquid levels. The static discharge head is the difference inelevation between the discharge liquid level and pump center line. The static suction head is thedifference in elevation between suction liquid level and pump centerline. If the static suction headis –ve the suction level is below the pump center line and it is called static suction lift.

Pressure head. It is the head due to pressure exerted by the discharge and suction points.

Friction head. Friction head is the equivalent head expressed in vertical feet of liquid pumpedthat is necessary to overcome the friction losses caused by the flow of liquid through this pipingetc. Friction head depends on the type of fluid, quality of fluid, size and type of pipes and fittingand interior conditions. Roughly it varies as the square of the capacity (flow).

Entrance and exit losses. When suction is from a reservoir, the point of connection of thesuction line and reservoir there is a loss due to sudden contraction and is called entrance loss. Awell designed bell mouth result in the lowest loss of pressure.

Likewise on the discharge side of the system when the discharge line terminates at some bodyof the liquid at the end of the piping this is called the exit losses. Generally the end of the pipingis of the same size as of piping and the difference in velocity head is entirely lost. In some casesthe end of discharge piping is a long taper so that velocity can be effectively reduced and the energyrecovered.

Velocity head. It represents the kinetic energy of a liquid per unit mass of fluid at any point,

expressed in ft-lb per lb of liquid of 2V

2gvh = When hv = vel. head in feet (ft lb/lb)

V = vel. in feet/sec

g = 32.2 ft/sec2

In high head pumps the K.E involved is relatively small but in low head pumps, it is relativelyhigh. Thus in case of high head pumps, failure to consider it in determing head will not appreciablyeffect the result.

In determining the head existing at any point, it is necessary to add the velocity head to thepressure gauge reading as the pressure gauge can indicate only the pressure energy while the actualhead is the sum of the kinetic (velocity) and potential (pressure energy) heads. Only in case wherethe suction & discharge line velocities are same (so also the velocity heads), the difference in suctiongauge and discharge gauge readings will show the total head. for a +ve suction pump.

Vapour pressure. The vapour pressure of a liquid at any given temperature is that pressureat which it will flash into vapour if heat is added to the liquid or conversely that the pressure at whichvapour at the given temperature will condense into liquid if heat is substracted.

Total head. The total dynamic head for a horizontal centrifugal pump is defined as follows.

H H HV2

V2

P P2 2

= − + − + −d sd s

d sg g

where Hd is the discharge head as measured at the discharge nozzle and referred to the pump shaftcenter line, feet. Hs is the suction head expressed in feet as measured at the suction nozzle andreferred to the pump center line. If the suction head is –ve the term Hs the above equation is positive.

The other two terms in the above equation are the velocity and pressure head at the dischargeand suction points respectively.

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CENTRIFUGAL PUMPS 137

The total dynamic head is the energy imparted to the liquid by the impeller of the centrifugalpump. If the discharge and suction heads can not be determined separately it is done by Bernoulli’stheorem. For complex systems involving both vacuum and pressure these are converted into absolutepressure expressed in feet of liquid.

For a vertical pump with the pumping element submerged, the total dynamic head is given by :

H H HV2

2

= + +d sd

g

where Hs is the distance from the suction liquid level to the center line of the discharge elbow andHd is the discharge head in feet referred to the center of the discharge elbow. The last term inequation represents velocity head at the discharge.

The various discharge and suction heads are given in figures 1 and 2.

Characteristic CurvesRising characteristic – head rises as capacity is decreased

Dropping characteristic – head at shut off is less than that at some capacities

Steep characteristic – large head increase as the capacity is decreased.

Flat characteristic – head varies slightly with capacity.

EFFICIENCYThe degree of hydraulic and mechanical perfection of a pump is judged by its efficiency. This

is defined as a ratio of pump energy output to the energy input applied to the pump shaft. The latteris the same as the driver’s output and is termed brake horsepower (bhp), as it is generally determinedby a brake test.

EfficiencyPump output

bhpW.H.P

bhp= =

QrH

550 × bhp=

where Q is capacity in cubic feet per second, r is the specific weight of the liquid (for cold water= 62.4 lb per cu ft) and H is head in fect. Qr is the weight of liquid pumped per second. If thecapacity is measured in gallons (US) per minute, equation becomes as below for water.

gpm × 8.33 × H gpm × He , WHP

60 × 550 × bhp 3960 × bhp= =

In above equation (gpm×H) /3960 it is the pump output expressed in horsepower and isreferred to as water horsepower (W.H.P).

If a liquid other than cold water is used, the water horse power should be multiplied by thespecific gravity of the liquid to obtain the pump output or liquid horsepower.

The pump efficiency as defined by above equation is the gross efficiency. This is used byengineers for the comparison of performance of centrifugal pumps. Besides this, there are a numberof partial efficiencies used by designers and experts, which describe only one phase of pump

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138 REFERENCE BOOK ON CHEMICAL ENGINEERING

performance - hydraulic, mechanical, volumetric - and are of no interest to the users of pumps butare important to the study of pump performance.

AFFINITY LAWSThese are based on relations between capacity, head and break horsepower. Pump head varies

directly as the square of the speed; the break horsepower varies directly as the cube of the speedand the capacity varies directly with the speed. The affinity laws are expressed by the followingequations.

2 31 1 1 1 1 1

2 32 2 2 2 2 2

Q H bhp= ; = ; =

Q H bhp

n n n

n n n

The affinity laws apply to each point in the characteristic curves. The letter n stands for speedand post script 1 and 2 stand for no.1 and no.2 pumps following the characteristic curves.

PUMP CONSTRUCTIONA centrifugal pump consists of a casing, impeller, casing wearing ring, gland packing, suction

and discharge nozzles and bearing supports with roller/ ball bearing. The impeller may be backwardvane type and the impeller may be open, semi closed or closed types. In backward vane impeller,head decreases as the through put increases; for forward vane impeller, head increases as the deliveryincreases. Open or semi open impeller is used for slurry handling ; for multi stage centrifugal pumps,the stage arrangement is made in such a way that the differential pressure between any two adjoiningstage chambers is kept to the minimum possible and several low pressure running joints are to bepreferred to a few number of joints subject to relatively high pressure. Also for multi stage pump,minimum leakage at running joints is kept and to maintain this for a long period of time and alsothe sequence of stages should be such as to avoid excessive complication in the formation of interstage passes.

N P S HIn the pumping of liquid, the pressure at any point in the suction line must not be reduced to

the V.P of liquid. The available energy that can be utilised to get the liquid through the suction piping,suction water way of the pump into the impeller is thus the total suction head less the V.P of liquid.The available head as measured at the suction opening of the pump has been termed N.P.S.H.

Example (i) water at 62°F and O suction lift (sea level)

N.P.S.H. = 33.9 – 0.6 = 33.3

(ii ) Do at 15 suction lift = N.P.S.H. = 33.9 – 0.6 – 15 = 18.3

Required N.P.S.H. It is a function of pump design and represents the min. required marginbetween suction head and the V.P at a given capacity. Required N.P.S.H, being a function of velocityat the suction passages and at the inlet to the impeller, increases as the square of the capacity.However, the available N.P.S.H. is reduced with increasing capacity due to friction loss in the suctionpiping. If suction pressure falls below vapour pressure of pumping fluid, there will be vapourisationof fluid and noisy operation of pump with drop in discharge pressure. This is called CavitationPhenomenon. The priming of a centrifugal pump is done by filling up casing with water till air isdriven out with discharge closed.

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CENTRIFUGAL PUMPS 139

SPECIFIC SPEEDThe basic definition of specific speed is that it is the speed (rpm) at which a theoretical and

geometrically similar pump would run if proportional to deliver 1 G.P.M against 1 ft total head withits best efficiency at these service conditions. Specific speed is an index of pump type.

Formula 3 4

QM

Hs

n=

where Ms = sp. speed, n = r.p.m, Q = G.P.M at speed n and H = total head per stage.

Normal sp. speed range for single suction impeller is 500 – 1500 r.p.m. The lower the specificspeed the higher is the head that can be developed for a total head and suction lift condition thespecific speed should not be below a certain value for successful operation. Limitation chart forspecific speed has been developed by Hydraulic Institute of U.S.A.

MECHANICAL SEALSThese are normally used for gland sealing in place of material like asbestos rope for stuffing

boxes of centrifugal pumps. Mechanical seals reduce gland leakages of fluid to a very low amountand it is used also when corrosive, hazardous and costly fluids are handled. These are spring loaded,flexible shaft mounted design and continuously and automatically compensate for shaft run out, axialend play, vibration & wear. Usually fitted with carbon disks–one rotating and one stationery, whichrestricts the gland leakage to a minimum. However a small leakage is desired for lubrication whenhandling liquid process fluids.

LOSSES IN CENTRIFUGAL PUMPLeakage loss: This reduces the volumetric efficiency due to leakage losses through the running

clearance between the rotating impeller and the casing parts. Leakage loss increases with the increaseof specific speed. In practice leakage loss is greater for smaller pumps because the clearance cannotbe reduced below a certain minimum; also because the wearing rings of larger pump are wider andco-eff. of discharge is smaller.

Disk friction loss: The particles of liquid in the space between the disk (impeller) and stationerywalls acquire a rotary motion. As a result of centrifugal forces, particles start moving outward inthe immediate neighborhood of the disk and new particles approach the disk near the center. Thepower consumption increases as the clearance between the disk and the wall is increased.

TECHNICAL LOSSESStuffing box and bearing losses. The friction loss in stuffing box is affected by size and depth

of stuffing box, pump speed, pressure and method of packing and lubrication. Friction torque is veryhigh with a tight gland but decreases rapidly as the gland is loosened and the leakage increases.Friction power losses increase approximately as the square of the speed. Pumps, with mechanicalseal stuffing box, losses are minimum. Bearing losses using properly lubricated ball bearing or rollerbearing, become minimum. Bearing lubrication and alignment is important to keep bearing losses atminimum.

HYDRAULIC BALANCING OF CENTRIFUGAL PUMPFor axial and radial balance in multistage centrifugal pump, some form of hydraulic balancing

devices must be used in the form of a balancing disc or a combination of these two. The balancingdisc of drum is nothing but a pressure reducing mechanism so used within the pump that thepressure differential across leakage joint is equivalent to the total pressure generated by the pump.

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140 REFERENCE BOOK ON CHEMICAL ENGINEERING

For double suction pump, the impeller is balanced by the discharge pressure as well as suctionpressure acting each in opposite direction. Double suction centrifugal pump is usually of highcapacity.

P S

AS

h = S – h – h + Ps fs i s

A S h = S – h – hs fs i

–h = S + h + hs fs iS

B

h = D–h –h + Ps fs i s

DA

CASE 1

CASE 2

CASE 3

CASE 4

Suction Heads of Centrifugal Pumps

P S

Fig. 1

Where S = Suction head : hfs = total friction loss in suction pipe, hi = entrance loss at AD = Suction static head and Ps = Pressure of enclosed place. hs = Suction head.Remarks : (1) A gage in suction line to a pump measures the total suction head (above

atmospheric)–velocity head at the point of attachment.(2) As a suction lift is –ve, vacuum gage will indicate the algebraic sum of total suction

lift and (–) velocity head.(3) If Ps in partial vacuum, the Ps in ft of liquid is to be expressed as –ve.(4) Suction lift or head are measured below or above atmospheric.(5) Use a foot value for suction lift with casing plug for air venting.

(6) The components in hs will be in consistent units.

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CENTRIFUGAL PUMPS 141

h = D + h + h + Pd fd e d

D B

h = D + hd fd

CASE 1

CASE 2

CASE 3

CASE 4

P d

BD

D

B

h = D + h + hd fd e

h = D + h + hd fd e

D

B

D

B

h = D + h + hd fd eCASE 5

Discharge Head of Centrifugal Pumps

Fig. 2

Where hd = Discharge head (in abs. press, and also Pressure in ft. of fluid)D = Static discharge head; hc = exit loss at B.Hfd = Total discharge pipe friction loss and Pd =Pressure gauge reading.

Remarks : (1) For horizontal pump datum for suction and dischrarge in pump centre line.(2) For vertical pump, datum is centre line of discharge line.(3) For comparatively short discharge lines, friction loss will be 10–20% of static head.(4) Discharge head will be given by pump discharge gauge.(5) The components in he will be in consistent units.

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142 REFERENCE BOOK ON CHEMICAL ENGINEERING

PUMP IMPELLER TYPESA. Forward curved vane—Head increases as the delivery rate increases

B. Backward curved vane—Head decreases as the through put increases.

The pump direction of rotation being clockwise (pump end). Suction and discharge heads ofcentrifugal pumps are given in Fig. 1 and Fig. 2.

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1. PRODUCER GASProducer gas is essentially a mix of CO and N2 together with H2, CO2, CH4 & O2 which are

present in small percentages. The gas is generated by blowing a mixture of air or air enriched withoxygen and steam through an incandescent bed of coal or coke or anthracite.

There are mainly two types of producer gas generators viz (i) Revolving body generator withfixed grate (exam. Wellman gas producer) and (ii ) Fixed body gas generator with rotating grate.

A. Wellman Gas ProducerThe rotating body is made of heat resistant steel and lined with refractory bricks. The ash is

discharged by the ash pan, rotating type, with water seal at the bottom and a stationery water cooledtop cover. An automatic water cooled poker is operated from top to keep the bed in uniformcondition of heat. Coal is fed from top by a mechanical feeder valve.

Pressurised air blast at 10" W.G by a turbo blower is introduced into the generator through abottom head. Both generator & ash pan rotate slowly and ash is discharged automatically by ploughsinserted in ash pan which dump it on the ash boxes. Steam at 0.3–0.5 lb/lb of coal or coke oranthracite is added to the air flow to (i) control of Clinker formation by increasing the air blastsaturation and (ii) to raise H2 rich gas by the water gas reaction. Major reactions in generator are.

(i) C + O2 = CO2

(ii ) H2O + C = CO + H2

(iii ) C + 2H2O = CO2 + 2H2

(iv) C + CO2 = 2CO

The producer gas temperature at exit is 1250 – 1500°C and pressure 1" W.G. The fuel bedis divided into four zones viz

(a) Ash Zone. It is just above the grate and the ash zone serves to preheat the incoming airblast from bottom.

(b) Oxidation Zone. Above the ash zone is the oxidation zone which is about 6" thick. Herereaction (i) takes place and the temperature is highest due to combustion reaction. Steam in air helpsto keep a lower temperature to prevent clinker formation. Heat released by combustion reaction mustbe sufficient to carry out endothermic reaction and compensate for heat losses by radiation. Thetemperature of oxidation zone is 1100–1200°C.

18INDUSTRIAL AND TOWN GASES

Chapter

143

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144 REFERENCE BOOK ON CHEMICAL ENGINEERING

(c) Above the oxidation zone is the top reduction zone. Primary and secondary zones whichis practically extend upto top of the fuel bed. The reduction reactions (ii ), (iii ) and (iv) take placein reduction zone and absorb potential sensible heat in the producer gas. The reactions (ii ) and (iv)are very fast as the gases enters the reduction zone. As the gases pass, CO2 and steam contentdecreases due to endothermic reactions & temperature of bed must be over 800 – 900°C as at thistemperature these reactions stop.

(d) Top heating zone. Here lies the freshly added charge of feed coal/coke/anthracite whichis dried & heated up by the incoming gases from reduction zone to start reaction as it descends toreduction zone. If coal is used, it is carbonised to coke liberating tar and volatile matter as well asSO2. Depending on sulphur present in coal, SO2 removal may be necessary to recover from producergas in subsequent purification stage. The bed temperature raises constantly apart from sensible andradiation heat losses.

B. Coppee Gas ProducerIt has fixed cylindrical body with rotating water sealed ash pan at the bottom which rotates

at the rate of 1 rev. in 10 minutes by a rack a pinion arrangement. There is no refractory brick injacket boiler. Air blast is introduced along with steam from bottom of the grate to increase air blastsaturation so as to generate more H2. Steam is generated from jacket waste heat boiler in annularspace provided in the body of the generator. The thermal efficiency of this generator is more.

1.2 Quality of gas generated depends on (i) air blast pressure (ii ) air blast temperature (iii )fuel size and type of fuel used and its quantity (iv) ash fusion temperature of fuel and steam/air ratio.

1.3 Producer gas output is around 120 MCF/ton of coal and its composition is as follows

CO = 24–28% (vol)N2 = 52–55H2 = 11

CH4 = 0.5CO2 = 4–5

The gross calorific value is 1068–1335 Kcal/m3 and density about 1.16 Kg/m3

1.4 Specification of Fuels for Producer GasCoal. It should be low in sulphur 1–1.2%, low in ash content but higher ash fusion temperature.

High volatile and weakly coking coals are preferable. The tar fog adds as much as 15 B.T.U/cft tocalorific value.

Coke and anthracite – Suitable for clean producer gas.

Typical composition of producer gas when using different feed fuels is given in page 145.

1.5 Operation ProblemsMaintaining correct depths of feed through out the fuel bed for uniform gas distribution so as

to prevent channeling and hot spots which lower the efficiency resulting in lower gas quality. Incoppee gas generator no clinker formation occurs due to low shell temperature of jacket boiler. Dueto poor quality of coal, ash discharge in Wellman producer may be problem due to clinker formation.Ash pan seal water is taken to a settling pond, clear water from pond is recycled along with makeup water. Gas temperature control from producer generator is important as a function of operationrequirement.

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INDUSTRIAL AND TOWN GASES 145

Fuels used

Composition Coal Coke Anthracite

CO 24–29% 24–30% 25–27%

H 11–15 11–14 14–18

CH4 0.5–2 0.5 1.2

Hydrocarbons 2–3 3–5 4–6

Nitrogen 52–57 52–55 50–53

Net Cal. Value, 1156–1352 1125–1201 1221–1299

Kcal/m3 at 60°F

at 30"Hg

Sp. gravity (air = 1) 0.9 0.9 0.9

N.B. 1. Air for complete combustion of producer gas and air mix (cold) is about 0.9 – 1.2 cft/cft ofmix.

2. The net calorific value of above mix is 578 – 640 Kcal/m3 and is less than coal gas air mixturehaving net calorific net value of 818 - 845 kcl/m3.

1.6 Industrial Use of Producer Gas

Application Type of fuel used Type of producer gas used

Heating coke ovens Coke Cold and clean gas

Regenerative furnace for Coal Hot raw gas

steels and glasses etc. manufacture

Heating retorts Coke Hot raw gas

Dilution for town gas supply with air Coke Cold and clean gas

1.7 Efficiency of Producer Gas GeneratorsBS-945 standard is normally used to determine the efficiency of producer gas generators as

given below.

Cold gas efficiency =Potential heatof gas

Totalheatof fuel×100

Hot gas efficiency =Totalheatof gasTotal heatof fuel

× 100

Total heat in the gas in the sum of potential heat calculated from gross and net calorific valuesplus sensible heat in the gas. All values are expressed as B.T.U/ton of dry fuel.

1.8 Gas Exit Temperature from GeneratorThis gives the gasification conditions in the generator. For example low gas exit temperature

may be due to one or more parameters as stated below.

(i) Fuel bed too thick

(ii ) Wet fuel

(iii ) Low gasification rate

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146 REFERENCE BOOK ON CHEMICAL ENGINEERING

(iv) Body surface temperature is too high (normal 50°C)

On the other hand a high gas exit temperature indicates.

(i) Fuel bed too thin or non-uniform fuel bed

(ii ) Channeling of hot gases in the bed with localized hot spots

(iii ) Producer gas is burning at the top

(iv) Ash zone is non even

(v) High gasification rate due to decrease in fuel cross sectional area because of the accumulationof clinker on sides and closing of air blast ports by clinker

(vi) Body surface temperature is too low (normal range is about 50°)

1.9 Cleaning of Producer Gas

When coke or anthracite is used, only water cooling in a packed tower is required followedby filtration in filter boxes packed with wood shaving and wood wool.

The filtering media may be mixed with iron oxide catalyst if H2S is present in producer gasgenerator from coke or anthracite. The washing tower is packed with 1-2" coke or lumps and wateris sprayed from top which cools the producer gas by a adiabatic cooling due to evaporation ofscrubbing water. The water removes dust particles from gas entering at the bottom of washing towerand the water dust mix then flows into a settling pond where m.u water is added and recirculated.

2. SLAGGING ASH PRODUCERThe ash is converted to molten slag due to intense heat generated using air enriched with

oxygen, in up run period. The fuel bed is deeper than conventional process and gasification rate ishigher, 500 lb/sft. Temperature control is effected by adding limestone or BF slag along with cokecharge. The operational problems are more due to molten slag, sticking on acid bricks refractory,causing choking.

3. WATER GAS OR BLUE WATER GASWater gas is primarily a mixture of CO and H2 together other small quantities of gases viz CO2,

N2 and CH4. The gas is made by passing steam on a bed of red hot coke.

3.1 The water gas generator consists of a tall vertical cylindrical vessel made of steel. The vesselis lined with refractory bricks, except in jacket boiler portion, where insulating bricks do notinsulate it. A rotating grate is provided at the bottom, which continuously removes ash into theash box. Air and steam is passed alternatively from bottom to the red hot bed and blow gasand water gas are obtained respectively from top of generator. The reaction with steam is asfollows.

C + H2O → CO + H2 ∆H = 52110 BTU/mole ...(1)

C + 2H2O → CO2 + 2H2 ∆H = 35420 BTU/mole ...(2)

The steam run is done, consequently, in both up and down directions through the red hot bedand water gas is collected alternatively from top and bottom of generator, followed by air up run,when the oxidation gases are vented to the atmosphere.

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INDUSTRIAL AND TOWN GASES 147

The reactions during air run are.

C + O2 = CO2 ...(3)

CO2 + C = 2CO ...(4)

The total cycle of operation lasts for 2.5–5 mins. The valves at the water gas off take linesat top and bottom of the generator, air valve, exhaust gases valve, steam valves for up and downrun, and rotary coke feeders valves are operated automatically through hydraulic devices. Run withsteam after air run with off gasses purged to vent, is also done in automatic sequence. LP wasteheat boiler steam is used for steam run; bed temperature during air run is 1100–1200°C. Thebed temperature comes down to 800–900°C during steam runs because of endothemic reactions(i) and (ii ) The exit water gas after seal box can be scrubbed with water and gas stored in gasholder. The dust laden scrubbing water, after settling in a pond, is released with m.u wateraddition.

3.2 Composition of Water Gas

H2 ----- = 45.51% (vol)

CO ----- = 45.40%

CO2 ----- = 3 – 6

N2 ----- = 3 – 7

CH4 ----- = 0.1 – 0.5

The water gas burns with a blue flame. The net calorific value is 2580–2758 Kcal/m3.

Sp. gravity (air – 1) =0.55

Theoretical bed temperature = 1900°C during air run

Actual bed temperature varies from 1100 – 1200°C during air run.

Factors for the quality generation of water gas are, quality of coke or anthracite, clinkerremoval efficiency, volatile matter & sulphur content of fuel and O2 enrichment of air can be avoided.The cycle timing is to be judiciously set.

The thermal efficiency of water gas generator is of the order of 60%.

3.3 Uses of Water GasIt is used in furnace operations when rapid heating is required. It is also a source of H2 gas.

The gas burns with a blue flame due to CO content.

4. CARBURETED WATER OR TOWN GASHere the water gas is enriched with hydrocarbon oil vapours (Diesel). The generator is similar

to water gas generator and water gas generated and oil vapour from a separate carburator, is mixedwith water gas followed by some cracking of some oil vapour in the super heater. Heat is suppliedby burning some oil vapour in carburator as well as in super heater.

In the carburator, preheated diesel oil is vaporised @ 2 US gallons per 1000 cft of carburetedwater gas which is generated by a water cooled burner at the top. Some cracking of oil also takesplace in the carburator whose temperature varies from 600–1000°C. The remaining cracking of oilvapour takes place in super heater, filled with chequer work. The gas leaves the super heater at about800°C. The heat required for cracking is generated by combustion of some oil in the super heater

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148 REFERENCE BOOK ON CHEMICAL ENGINEERING

and also by blow gas during the blow period so as to raise the temperature of carburator and superheater. Super heater top temperature is 650°C and bottom temperature is about 800–900°C. Theoutgoing gas is cleaned by water cooling in a scrubber and stored.

The composition of carbureted water gas is.

H2 = 37% (vol)

CH4 = 14

Ethane etc.

CO = 30.5

CnHm = 7

CO2 = 5.6

N2 = 5.5

Oxygen = 0.4

The gross calorific value is 4450 Kcal/m3 and net calorific value is 4075 Kcal/m3.

Sp. gravity (air = 1) is 0.63. The overall thermal efficiency is 80%.

Use of Carbureted water gas.

It is mainly used as a town gas for domestic consumption.

4.1 Semi Water GasIt contains almost equal concentrations of H2 and CO more than those in water gas or B.W.G

to suit ammonia synthesis gas generation (H2 and N2 in the ratio of 3:1). The gas generator is withjacket boiler and rotating ash grate. The coke feed mechanism is done by automatic system andreversing mechanism, by hydraulic controller like those of water gas generator. This has up runperiod with auxiliary air to suit the production of necessary N2 for ammonia synthesis after purificationand CO conversion. The composition of the gas is as below.

H2 = 34.2% (vol.)CO = 36.1

CO2 = 7.4N2 = 21.5

CH4 = 0.8H2S = 0.03

Coke/cft SWG = 1.3 – 1.4 kg

Calorific value = 1700 Kcal/m3

Coke used is about 4" size. Cold gas efficiency = 65%.

The cycle of operation of the generator proceeds in the following sequence as per hydrauliccontroller.

(a) Blow run – Primary air is blown up from bottom to bring up the temperature of bed tored-hot. The combustion gases are vented through stack.

(b) Up run steam – Preheated auxiliary air along with L.P steam is blown from bottom & semi-water gas is collected from top of the generator. Reactions;

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INDUSTRIAL AND TOWN GASES 149

C + H2O → CO + H2 ...(i)

C + 2H2O → CO2 + 2H2 ...(ii )

CO2 + C → 2CO ...(iii )

Reaction (i) is very rapid and stops when bed temperature is reduced to 800–900°C.

(c) Down run steam – Here L.P stem is blown downwards and semi-water gas is collectedfrom bottom.

(d) Final up run. Primary air is blown from bottom to remove remaining CO, H2 etc. and ventedto atmosphere, as well as raising bed temperature uniformly. Ash from slow moving rotating grateis discharged into ash boxes from where it is periodically removed. The sequence time variesbetween 3–5 mins. The primary air, auxiliary air, steam change over and vent stack valves are openedand closed as per operation sequence by hydraulically controlled automatic controller, working at 850- 950 psi through cam action, which controls power cylinder operation, attached to each value forthe operation sequence.

The exit gas at 550 – 650°C from generator is passed through a water seal box and thenwashed in a Lymn washer tower with 0.7% Sodium Carbonate soln., which removes dust and coolsthe gas. The dust laden wash water is passed into a settling pond, which removes ash dust and topwater is sent to a cooling tower after adding make up water and re-circulated. The hy. oil controllerconsists of power cylinder, double restriction value, throttle valve and interlock control valve.

For the production of ammonia synthesis gas, the water gas is passed through series of Ironoxide catalyst boxes, mixed with wood shavings when H2S is absorbed and stored in gas holder.

The water gas for ammonia production is then treated in 2 stage shift reactors for CO removalin primary and secondary rectors so as to get ammonia synthesis gas with little CO, which isremoved in ammonia plant. The CO conversion catalyst contains Fe2O3 = 93.3%, Cr2O3 = 3 – 8%,K2O = 2.07% & Al2O3 = 0.8%.

Semi water gas is exclusively used for the production of ammonia synthesis gas.

5.0 BLAST FURNACE GAS. (B.F)About 60% of the heat in coke comes out in the exit gases from a Blast fumace during pig

iron production. This gas is called blast furnace gas and has the composition as follows.

CO = 27% (vol)

H2 = 2

CO2 = 11

N2 = 60

The net calorific value of the gas is 800–934 kcal/m3. Out of total heat available in B.F gasupto 80% heat is utillized in the steel plant and remaining 20% of the total heat is available as surplus,which is generally used in coke oven battery; heating boilers, reheating stoves etc.

5.1 Cleaning of the B.F. gasThe dust, associated with B.F gas, consists of mainly coke, iron oxide and lime. The conc.

of heavy dust can be 1000 gms/100 cft and that of fine dust (< 5 µ) is 5 gms/100 cft. Less vigorouscleaning of gas is required for use in L.P boilers and reheating stoves.

There are two processes for dust cleaning.

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150 REFERENCE BOOK ON CHEMICAL ENGINEERING

Dry process: The gas from down comers of blast furnace is taken into a dust settling chamberwhere heavier dust particles settle down and conc. of dust is reduced to 10–100 grains/100 ft3.

The gas is then filtered in automatic bag filters and dust conc. is further reduced to 1 grain/100 cft.

Wet process: The gas from the blast furnace is scrubbed with low and high pressure spraysin a water scrubbers fitted with baffles and cross partitions followed by separation of entrained waterdroplets from saturated gas in an electrostatic precipitator. Water requirement for sprays is 24 USgallons/100 ft3. The scrubbed water slurry is thickened in a thickener and the clear water isrecirculated after make up water addition.

6.0 COAL GAS

Coal gas is produced from H.T., LT and CVR carbonisation of coal for the production of coke.

Coal gas by H.T coal carbonization process.

Crushed bituminious coal to 3 mm size is fed to silica brick lined particular oven of the cokeoven battery by larrycar as per charging and discharge series of coke ovens. The top cover of theoven is replaced on the top of the oven and heating of coke oven is started through about 31 flues(depending on capacity) on each side by coke oven gas from both sides of the oven. At the endof 15–16 hrs of combustion, the temperature inside the oven reached to 1100–1200°C which is thetemperature for H.T carbonization of coal. The typical size of each oven, length between doors ±12900 mm. width 345–375 mm and height = 3100 mm for a 30 oven standard battery. The widthof oven gives the carbonisation time approximaely @ 1 hr per 25 mm.

Coke oven gas comes out of the ovens at 600–800°C and is cooled to 80–90°C by spray ofself produced ammonia liquor in the hydraulic main when major portion of tar is condensed and gasand liquor are separated in the separating box. From the separating box tar is sent to storage andammonia liquor neutralised with sulphuric acid to produce ammonium sulphate by crystallisation andis separated by centrifuging.

Coke oven gas then enters the primary cooler when remaining tar and some naphthalene separateout. The gas is then pressurised in a centrifugal blower which, after cooling and tar separation in a tarcatcher; the coke oven gas is then scrubbed in ammonia scrubbers, packed with R/R.

After separation of ammonia, the gas is sent to benzol tower where it is washed with regeneratedwash oil, which is sent for recovery of coal carbonisation products. The gas after benzol recoveryis sent for coke oven heating or synthesis gas making or any other heating requirement.

After carbonisation, red hot coke is pushed out of oven by combined stamping by ram pushermachine including door lifting mechanism. The red hot coke is pushed to a quenching car and takento a quenching tower where it is cooled by spraying water and coke discharged to wharf.

6.1 Coal SpecificationF. Carbon = 51% (vol) by diff.

V.m = 27

Moisture = 4

Ash = 17

Sulphur = 0.7

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INDUSTRIAL AND TOWN GASES 151

Calorific value of coal is about 6300 Kcal/kg

Coal per ton of coke = 1.5–4 MT/MT coke

Coke oven gas composition.

H2 = 55.7% (vol)

CO = 5.4

CH4 = 24.0

CnHm = 1.6

CO2 = 2.2

N2 = 5.3

O2 = 0.4

H2S = 2.3 gm/NM3

Coal gas output = 265 NM3/MT coal

The net calorific value = 4029 Kcal/m3

The density of coal gas (air = 1) = 0.49

Analysis of coke.

Moisture = 4.5 %

Ash = 23 – 24

V.m = 1.5 – 2

Sulphur = 0.5

F.C = 73 – 74 (by diff.)

Ash fusion temperature = 1350 – 1410°C

Calorific value of coke = 5890 Kcal/kg

Crude Benzol output = 12.0 lit/MT of coal

Coal tar output = 3.5% of coal carbonized.

Uses of Coke

Gas coke from less coking coal or blends is used for gas generation viz water gas, town gasetc. Met. coke is used in metallurgy. Met. coke is less combustible than gas coke.

7. NATURAL GAS

Natural gas is obtained is association with crude oil from oil wells (it is also available from gaswells). After separation of crude oil in a series of separators, natural gas is transported through pipelines after compression to desired level in NG fired gas engines coupled to NG compressors. Usuallyoil companies use a battery of such NG compressors.

The quality of NG depends on the type and location of source. Usually it contains mainlymethane (CH4), associated higher HC viz ethane (C2H6) (alkanes), Propane (C3H8), butane (C4H10),pentane (C5H12) and hexane (C6H14), together with Nitrogen, CO2 and sulphur compounds (ppmlevel).

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152 REFERENCE BOOK ON CHEMICAL ENGINEERING

Raw natural gas is usually stripped of alkanes upto butane & propane for production ofLiquified Petroleum Gas (LPG) for mainly domestic use by low temperature gas fractionationprocess while pentane is separated from N.G by absorption in a solvent. Analysis of treated N.G isas follows.

CH4 = 85–91%

C2H6 = 6.3

C3H8 = 1.15

CO2 & N2 = 1.55

Sulphur = 20 ppm

The net calorific value of N.G. is 9001 Kcal/NM3. Natural gas is used either as a fuel or asa source of hydrogen; when propane and butane are not separated from NG it is called associatedgas.

(i) Natural gas thus stipped of LPG constituents & Pentane content, can be liquefied to facilitatetransportation by ocean going refrigerated bulk carriers as liquefied natural gas which is then storedin shore based refrigerated liquid NG storage facilities in destination country where it can be re-gasified to natural gas for use mainly as a fuel or other uses. Alkanes upto butane (C4H10) isgaseous, pentane (from C5H12 to C16H34) are liquids upto 20°C and the rest are solids.

(ii ) Liquification of natural gas for LNG.

Because of high critical pressure (47.3 kp/cm2) of methane, liquification of natural gas by usualcompression and cooling method is difficult and uneconomic.

The critical temperature of methane is –82.5°C and B.P and heat of evaporation are –164°C(at 760 Torr) and 121.9 Kcal/Kg respectively.

There are few processes for LNG manufacture described elsewhere in this book.

(iii ) Typical analysis of associated NG without LPG extraction (Upper Assam)

CH4 = 77.9% (vol)

C2H6 = 9.38

C3H8 = 6.01

C4H10 = 2.75

C5H12 = 0.69

N2 = 0.42

CO2 = 2.85

Specific gravity = 0.739

Mol. Weight = 21.43

NCV Kcal/nm3 = 10484.

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INDUSTRIAL AND TOWN GASES 153

PHYSICAL DATA/GRAPHS

9000

8500

8000

7500

7000

10 20 30 40 50

Volatile m atter (% )

H c

lean

coa

l (K

cal/k

g)u

Calculation of Calorific Values or Solid Fuelfor b itum inous coals containing 5–45% volatile matter

Fig. l. Graph for calculation of calorific values of solid fuels.

Hu clean = 8150 + 38.83 (A + W) – 1.1806 (A + W)2

A ash content, %

W water content, %

100 (A + W)× volatile matter of clean coal = volatile matter of raw coal.

100

Conversion of gross into net calorific value H0 into Ha (raw coal) for solid and liquid fuels.

Hu raw = HO raw – 5.85 (0.09 H + W) kcal/kg. (H = hydrogen content. %)

When the moisture content alters from w1 to w2 the net calorific value (raw coal) becomes

Hu2 = (Hu1 + 6 w1) 2 2

1 1

100 A W

100 A W

− −− − – 6W2 ; A2 =

21

1

100 WA

100 W

−−

For coke, Hu clean = 7,950 kcal/kg

For wood and wood shavings, Hu raw = 4.950–51.9 W

Source : Borsig pocket book 3rd edn. 1970.

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154 REFERENCE BOOK ON CHEMICAL ENGINEERING

20001000

40003000

60005000

80007000

95009000

60

50

40

30

20

10

10

20

30

40

50

60

Net calorific values Hu (kcal/kg) of C lean and Raw C oal

70

5000

6000

7000

8000

Hu for raw coal (kcal/kg)

Wat

er c

onte

nt (

W)

(%)

Ash

+ W

ater

con

tent

(A

+ W

) (%

)

H = Hu ra w u cle a n

100 – (A + W )

100– 6 W

H clean = 9000 kcal/kg

u

Fig. 2. Graph for net calorific values of clean and raw coal.

Example : For bituminous coal with Hu clean = 7750 kal/kg, A = 25% and

W = 15% (so that A + W = 40%) we obtain Hu raw = 4,560 kcal/kg

Note : Hu = net calorific value (Ho = gross calorific value).

Source : Borsig pocket book 3rd edn. 1970.

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INDUSTRIAL AND TOWN GASES 155

0 200 400 600 800 1000 1200 1400 1600 1700

0.32

0 .34

0 .36

0 .38

0 .40

0 .42

G as tem pera tu re (°C )

16% CO 2

12%

8% 16%

12%

8%

400350300250200150

10050

Hard coal (B itum linous coa l)

Cp (true spec, hea t) Cpm (m ean spec, heat be tween 0 and t c)o

H = 7577 kcal/kgu

i = kcal/nm3

Spe

cific

Hea

t (kc

al/n

m°C

)3

0 200 400 600 800 1000 1200 1400 1600 1700

0.32

0 .34

0 .36

0 .38

0 .40

0 .42

G as tem pera tu re (°C )

A ir ratio n = 1.1

1.5

1.9

400350300250200150

100

Coke-oven Gas

H = 4685 kcal/kgu

i = kcal/nm3

Spe

cific

Hea

t (kc

al/n

m°C

)3

Fig. 3. Specific heat-gas temperature relationship for hard bit. Coal and coke oven gas.

Source : Justi, E, Specific Heat, Enthalpy, Entropy and Dissociation of Industrial gases, © Springer Verlag1938.

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156 REFERENCE BOOK ON CHEMICAL ENGINEERING

0

0

200

200

Natural G as

400

400

600

600

800

800

1000

1000

1200

1200

1400

1400

1600

1600

0.32

0 .32

0 .34

0 .34

0 .36

0 .36

0 .38

0 .38

0 .40

0 .40

0 .42

0 .42

0 .44

0 .44

G as tem pera tu re (°C )

G as tem pera tu re (°C )

1.1

1.3

1.0

1.0

1.3

1.31.1

400400

600600

500500

350350

300300

250250

200200

150150

10010050

H = 7475 kcal/nmu3

H = 10800 kca l/kgu

i = kcal/nm3

i = kcal/nm3

Spe

cific

Hea

t (kc

al/n

m°C

)3

Spe

cific

Hea

t (kc

al/n

m°C

)3

A ir ratio n = 1 .0

A ir ratio n = 1 .0

Fuel o il----------Cp (true spec, heat)----------Cpm (m ean space, hea t between 0 and t c)o

1 .1

1.3

1.1

1 .1 1.1

Fig. 4. Specific heat-gas temperature relationship for fuel oil and natural gas.

Source : justi, E, Specific Heat, Enthalpy, Entropy and Dissociation of industrial gases © Springer-Verlag.

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INDUSTRIAL AND TOWN GASES 157

2000 3000 4000 5000

Net Calorific value Hu (kcal/kg): Boie, W. Energietechnik. Sept. 1953Source

Spe

cific

air

and

Flu

e-G

as V

alue

s V

L :

V (

NM

/Kg)

0G

3

6000 7000 8000

17

16

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

V 1.01 nL nm kg3 /Hu + 550

1000

Vg (1.01 n–0.106) + 1.17 nm kg3 /Hu + 550

1000CO max

CO 2

2

A ir ratio n =

E xa m ple :H u = 5 200n = 1 .4A = 1 0%

L = 5 .8 1 - L010 –616 9

10 –616 9

= 5 .786 nm 3/kgV L = 1 .4 - 5 .78 6 = 8 .1 n m /kg3

V G = 8 .69 - [3 + (1 .4 - 1 )]

8 .5 88 n m /kg3

Air ra

t io N

= 2

.0 1

.9 1

.7 1

.6 1

.5 1

.4 1

.3 1

.2 1

.11.

0V L0

Vg

S p ec if ic a ir a n d flue g a s v o lum esfo r h a rd (B itu m in ou s ) an d so f t (B row n) C o a l

T he g ra ph is va lid w ith a m ean ash co nten t A o f 6% and m ea n C O M a x 1 8.9% .2If A 76% th e va lu e taken from the d iag ra m mus t b e reduced b y a correc tion fac torK as fo llow s : spec . a ir vo lum e V by K = and spe c flue g as vo lum eLO

T he curve s a re not va lid for coke, w o od pe at.

V by K = [3 + (n –1)]. W hen A < 6% the sam e value a re use d for ca lcu la tionG

A– 6A– 6 169

169

1.8

Fig. 5 Specific air and flue gas volumes for hard bit and soft (brown) coal.

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158 REFERENCE BOOK ON CHEMICAL ENGINEERING

1.0 1 .2 1 .4 1 .6 1 .8 2 .0 2 .1

30

40

50

60

70

Air Ra tio n

D e w - p o in t t e m p e r a tu r e o f f l u e - g a s e sT h e gra ph b e lo w sh o w s th e flu e-ga s d e w -p o in t te m p eratu re s o f v a riou s fue ls , o n ly ste am(w ater v a po u r) c o nd e n sa tion be in g ta ke n in to a cc o un t. T h e v alu es a re ba sed o n a n 8 0 %re lat iv e h um id ity o f the fu rn a ce a ir a t 20 °C

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Dew

-Poi

nt (

C)

R h in e la nd B ro w n C oalC en tra l G e rm a n Brow n C oal

W o od, p eatD rie d B row n C oal 1 5% w ater

6 0% w ater

5 2% w ater

B itu m inous C oal

B la st-furna ce G as

0 1

0.5 %

1

S ulphur con ten t o f fiel o il 3%

1.5

2

2.5

2 3 3 .550

100

150

W h e re su lp h ur is p re se n t in th e fue l, the d e w -p o in t is c o ns id e ra b ly a ffe c te d b y th e c om b u s tio n o f th esu lp hu r c on ta ine d in the flu e - g ase s. T h e d ia g ra m w h ich sh o w th e de w -po in t tem pe rature fo rd iffe ren t su lph u r-c on te n t va lu e s in th e fu e l-o i l.

S o urc e fo r w ater d e w -p o in t : G um z, fue l an d f ir in g te c hn o lo g y,S p ring e r Ve r la ng 19 6 2 © so u rc e fo r a c id d e w -p o in t : G la ub i tz ,V G B -H ef t 68 . 1 9 60 .

D ew P o int of the f lue gases w ith S O2

Dew

-Poi

nt°C

)

F ig . 6 . D e w po in t tem p e ra tu re o f f lu e g as fo r v a riou s so lid fu e ls/B F ga s a nd su lp h u r b e a rin g f lu e g ase s from fu e l o i ls .

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19LNG PRODUCTION

Chapter

1. Because of high critical pressure of methane, liquified natural gas LNG cannot be producedby compression and cooling economically. The critical pressure and temperature of methaneare 47.3 Kp/cm2 and –82.5°C respectively and B.P and heat of evaporation being –164°C (at760 Torr) and 121.9 kcal/Kg. LNG is produced by cryogenic process.

2. Pretreatment of natural gas mainly methane, mixed with other paraffins, is necessary toremove sulphur compounds and other components that would either freeze out, thus restrictingthe flow of natural gas, or will lead to pollution upon combustion after reevaporation ofL N G.

3. N G liquefaction processes.

The commonly used processes are (a) Baseload liquefaction process and (b) Cascade Processof cooling using three refrigeration loops of propane (B.P = –44.5°C at 760 Torr), ethylene(B.P = – 103.9°C at 760 Torr) and methane (B.P = –164°C at 760 Torr).

3.1 In base load liquefaction process, heat is to be removed from N G to cool it to –160°C byrejecting heat to atmosphere or water. This is an efficient process suitable for large scaleL N G production.

3.2 In cascade liquefaction process using 3 refrigerant loops of propane, ethylene and methane,each refrigerant supplies refrigeration at discrete temp level. This process has nine stagerefrigeration.

Physical data for propane, ethylene and methane are as follows.

Critical temp Critical press B. P Heat of evaporation°C Kp/cm2 °C Kcal/kg

Propane : 96.8 43.5 –44.5 101.8

Ethylene : 9.5 51.7 –103.9 125

Methane –82.5 47.3 –164 121.9

4. CASCADE PROCESSCascade process of refrigeration uses separate loops and suitable refrigerant for each loop. The

refrigerant in L.P circuit is condensed by evaporating next higher temperature (B.P) circuit refrigerantin the cascade evaporating cooler or in other words, the refrigerating effect of higher temperature (BP)circuit is used to remove heat of condensation from lower temperature (B.P) circuit. In short, only thecascade evaporating cooler with lowest evaporating temperature generates the reqd. refrigerating effect.

159

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160 REFERENCE BOOK ON CHEMICAL ENGINEERING

In natural gas liquefaction, three temperature (B.P) levels form nine cascades using threerefrigerant cycles of propane, ethylene and methane, each of three stages. The methane refrigerationloop is open due to the fact that it is combined with N.G feed and after final let down in flash vesselsliqued methane forms part of LNG production. The flowsheet is given in Fig 1.

Fig. 1 Cascade Process for LNG Production.

Each of these three temperature levels (B.P) corresponds to preset pressure let down in flashvessels (D) for evaporating the refrigerant in heat exchange with N.G feed and separate propanerefrigerant stream in propane evaporating cooler (E) and then to ethylene evaporating cooler (E). In thisprocess heat is removed from NG at successively lower temperature and heat is rejected to coolingwater or air via warmest refrigerants, generally propane and after compressions and after flash cooling(B), liq propane refrigerant is stored in tank (c) and compressed ethylene gas, after water cooling, issent to propane evaporator for cooling, followed by cooling and condensation in ethylene evaporatorcooler (E).

After ethylene evaporator, N.G is condensed and after flashing in flash vessels (D) temperatureof liquid N.G falls, liquified and separated and stored in refrigerator vessels. The evaporated N.Gfrom flash vessels is recycled via ethylene evaporator cooler and is fed to methane compressorsuction, compressed and after cooling, N.G meets the make up N.G. stream and the process goeson.

Flash coo lerB

C

Drive

Propane After coolercom pressor

After cooler

D rive

Ethylene com pressor

Flash vesse lD

Evaporatingcoo le r E

LNG

Flash vesse lD

Flash vesse lD

Evaporatingcoo le r E

After cooler

N . G . Feed

M ethanecom pressor

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LNG PRODUCTION 161

Liq. N.G is transported by refrigerator tanker or trucks. For transportation by ships, N.G isunloaded in on-shore refrigerated LNG storage tanks; from where it is evaporated by steam heatingand NG is distributed to end users through pipe lines.

Processing N.G before LNG ProductionNatural gas is freed from CO2, moisture and if sulphur is present and it is to be sweetened.

Sp. enthalpy of evaporation Volumetric refrigerating

at std B.P. kj/kg effect at –15°C to +30°C kg/m3

Propane 439 2238

Ethylene 48 1995

5. STORAGE OF LNG

Double integrity tank with suspended inner tank of concrete lined inside with S.S is used.Lining material is 9% Nickel and 5000 series Al metal.

6. LNG DATA(i) 0.035 m3 at 111 °K is derived from 18 m3 of LNG. Storage temperature of LNG is 170°K

at 2.24 Mpa (325 PSIA).

(ii ) Heat of vapourisation of LNG is 232 Mj/m3 of LNG at 0.1 Mpa. Heat required forregasification of LNG is 0.3 KJ/m3 of gaseous NG.

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162 REFERENCE BOOK ON CHEMICAL ENGINEERING

20PRODUCTS MANUFACTURED

FROM BENZENE, ETHYLBENZENE, ETHYLENE, ETHYLENEOXIDE, ETHANOL AND OTHERS

Chapter

A. PRODUCTS MANUFACTURED USING BENZENE AS RAW MATERIAL1. Styrene → Polystyrene

A B S resinS B R / LatexPolyester resinsSAN resin

2. Cyclohexane → Adipic acid → Hexamethylenediamine↓ ↓

Cyclohexanol Caprolactum → NylonCaprolactum

3. Cumene → Phenol → Bisphenol AAcetone → Methyl metha-crylateCellulose acetate (adsorbent)Methyl isobulyl ketoneMethyl Phenyl ketoneAldol chemicals (Hexamethylene glycol)

4. Nitrobenzene → Aniline → Aniline isocynate↓

Polyester resin5. Malic anhydride → Polyester resins6. Chlorobenzene → DDT → Insecticides

↓Phenol

7. Anthraquinone → Dyes

162

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PRODUCTS MANUFACTURED FROM BENZENE, ETHYLENE, ETHYLENE OXIDE... 163

8. Dichlorobenzene → hexachlorobenzene (BHC)9. Dodecyl benzene (for detergent use)

10. Benzene Sulphonic acid11. Glyoxal12. Benzaldehyde13. Propyl benzene → Isopropyl benzene14. Lindane ( Y isomer of BHC)

B. ALCOHOL, C 2H5OH (ETHANOL) GRADES

Purity %Vol.(i) Industrial alcohol = 96.5

(ii ) Denatured* alcohol = 88(with methanol)

(iii ) Fine alcohol (Pharma use) = 96–96.5(iv) Potable alcohol = 43(v) Absolute alcohol or rectified spirit = 99.7–99.8(vi) Gasol (Gasoline with alcohol) = 98% gasoline with 2% alcohol*

*Gasol also used in some south American countries with Methanol in the proportion of2.5–5% methanol and rest gasoline.

“Proof” of Alcohol

U.K : Proof 87.7 equals 50% concentration at 10°C.

U.S.A.: Concentration is 12

of proof at 15°C.

N.B. Indian whisky is 75° proof (42.8% conc.)

C. PRODUCTS MANUFACTURED USING ETHANOL AS RAW MATERIAL

1. Vinegar2. Acetaldehyde/Acetic acid3. Ethyl acetate4. Ethyl chloride/bromide5. Other Ethyl esters6. Ethyl amines (for rubber processing)7. Sodium ethoxide8. Acetic anhydride9. Dyes and intermediates

10. Diethyl ether11. Glycol diethylethers and others12. Xanthenes13. Drugs and medicinal chemicals14. Organo-silicon products15. Synthetic resins

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164 REFERENCE BOOK ON CHEMICAL ENGINEERING

D. ETHYLENE OXIDE IS USED FOR THE PRODUCTION OF :(i) Methyl hexanol → Defoaming/wetting agents and plasticiser

(ii ) Penta erythritol → Alkyd resins, explosives, Moulding powder

(iii ) Trimethyl propane → Alkyd coalings, lube oil additive, Textile finishes & Urethanefoam

(iv) Acetic acid → Acetic anhydride,→ Aspirin, Vinyl acetate, Cellulose acetate.

→ Acetyl Chloride → Organic synthesis and dye. Chloroaceticacid → Sod. carboxy methyl cellulose, ethyl acetate,Thioglycolic acid herbicides.

→ Cellulose acetate

→ Acetate salts → Flavours, perfumes and solvents.

→ Vinyl acetate → PVC acetate and Poly Vinyl acetate.

(v) Per Acetic acid → Bactericide, Bleaching agent, Fungicide, Organic Synthesis,Polymerisation and Catalysts.

3. Ethylene dibromide → Dyes, Fumigant, medicines, Tetra ethyl lead (scavengers)

4. Diethyl Ketone → Solvents.

5. Polyethylene → Electrical Cables, Pipes, fittings, containers, etc, monofilamentfilm and sheet moulding powder and granules.

6. Mono, di-and Tri Ethanol amines.

7. Vinyl toluene → Surface coatings.

8. Ethyl alcohol → Acetaldehyde, ethyl ether, chloroform, Dimethyl amine, ethylacetate, Ethyl bromide Ethylene dibromide, glycol ethers.

9. Ethyl Chloride → Anaesthetics, Ethyl cellulose, TEL.

E. ETHYLENE DICHLORIDE

→ Ethylene diamine, adhesive, Corrosion inhibitors, rubber latexstabilisers and Textile lubricant.

→ Agri-fumigant, vinyl chloride

→ Fibres, plastics.

→ Tichloro ethane → Vinyl iodine chloride → fibres, filamentsand plastics.

→ Ethylene amine → Tri ethylene di-amine, Urathane foam,Catalyst. Flocculant, pesticides, and surface active agent.

→ Poly ethylene amines, → Adhesive corrosion inhibitors, paperprocessing and deemulsifiers

10. D E A → Formalin.

F. PRODUCTS FROM ETHYLENE PRODUCED FROM NAPHTHA1. Ethyl benzene

2. Ethylene Oxide

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PRODUCTS MANUFACTURED FROM BENZENE, ETHYLENE, ETHYLENE OXIDE... 165

3. Ethylene dibromide

4. Diethyl toluene (Solvent)

5. Poly ethylene (Plastics)

6. Ethyl alcohol

7. Ethyl chloride

8. Ethylene dichloride

9. Ethylene amine

G. PRODUCTS FROM ETHYL BENZENE

1. Acetophenone → Perfumes

Pharmaceuticals

Solvent

2. Benzoic acid → Benzyl benzoate

Phenol

Sodium benzoate

Plasticizers

Perfumes

Flavouring chemicals

Pharmaceuticals

3. Styrene → Polystyrene (Plastics)

S B R rubber

Chlorostyrene → Flame retardant resins

Alkyd Polyester resins

SAN (Plastics)

Styrenated oils

4. Diethyl benzene → Drying oils

Elastomers

Resins

5. Ethyl anthraquinone → H2O2 →Peroxide chemicals as bleaching agent

6. Ethylene Oxide → Nonionic detergent

Polyester (Dacron)

Ethyl Glycol (antifreezing agent)

As solvent for quick drying varnishes and enamels

7. Ethylene dibromide → Dyes

Fumigant

Pharmaceuticals

Tetraethyl lead (TEL) scavenger

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8. Ethyl alcohol → Hard drinks

Acetaldehyde

Ethyl ether

Chloroform

Diethyl amine

Ethyl acetate

Ethyl bromide

Ethyl chloride → Ethyl cellulose

Ethylene dibromide.

Glycol ether

9. Ethylene dichloride → Ethylene diamine

Vinyl chloride → PVC

Fumigant

Tetrachloromethane → Chloride, vinyldine

10. Ethyleneimine Triethylene diamineUrethane foamFlocculantPlasticizersSurface active agentPolyethylene amines

11. Acetaldehyde → Acetic acid → Acetic anhydrideAcetyl chloride (Dye)Chloroacetic acidCellulose acetateVinyl acatatePVAAcetate esters(Flavour, Perfume and solvents)

12. Chloroacetic acid → HerbicidesSod. carboxy celluloseEthyl acetateThio glycolic acid

13. Ethylene diamine → AdhesiveCorrosion inhibitorsStabilising agent for rubber latex,Textile lubricant

14. Polyethylene amines → Demulsifying agents, adhesive

corrosion inhibitor and paper work

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Five type of pigments from synthetic iron oxide can be made with varying tints of red, yellow,orange, violet and red.

A. Manufacture of Iron Oxide Pigments by Roasting Process

Synthetic iron oxide is prepared by (i) roasting iron pyrites for 4 hrs. at 600°C, (ii ) roastingferrous sulphate for 9 hrs. at 700°C and (iii) Ammon. ferrous sulphate at 700°C and then furtherroasting for 3 hrs at 100°C and calcining α Fe2O3 (red haematite ore).

Various colours of synthetic iron oxide can be made by roasting hydrated Ferrous Sulphate saltmixed with other salts for use as pigments. It is also made by calcining α Fe2O3.

(a) Zinc and Al. sulphate gives orange-red colour.

(b) Calcining FeSO4 at lowest possible temperature gives dull red colour. Two stage calcinationgives brighter colour and by product Na2SO4 can be made by absorbing SO2 gases in soda solution.

(c) Calcining FeSO4 with Mn salts at higher temperature gives blood red colour to darkercolours.

Reactions:

FeS2 + 2H2O + 7O2Heat→ FeSO4 + H2SO4

2FeSO4Calcining→ Fe2O3 + SO2 + SO3

FeSO47H2O → FeSO4 H2O + 6H2O

6FeSO4H2OHeat

650°C→ 2Fe2O3 + Fe2(SO4)3 + 6H2O + 3SO2

Fe2(SO4)3 → Fe2O3 + 3SO3.

Ferrous sulphate is usually made from pickling of iron scraps with sulphuric acid and crystalisingsalt:

Fe + H2SO4 = Fe2O4 + H2.

Heating of Ferrous Sulphate in presence of air:

6FeSO4H2O + 3/2 O2 — 3Fe2O3 + 6SO3 + 6H2O.

21Chapter

SYNTHETIC IRON OXIDE PIGMENT

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B. Manufacture of synthetic iron oxide pigments having soft pure colours is done by precipitation and hydrolysis process

Precipitation process gives soft pigments with bright hue. The process consists of removingexcess pickling H2SO4 in mother liquor, left after acid pickling of iron scrap. The liquor is neutralisedwith scrap iron. The solution of iron salt (FeSO4) is then mixed with NaOH in an open seed reactionvessel with oxidation by air at a temperature of 20–25°C. Alkali is used in such a way that thesolution remains acidic pH. The reaction time is 10–100 hrs. depending on temperature, kept(10–90°C), and desired crystal size of FeSO47H2O is achieved. The precipitate is yellow pigment (α-FeOOH-Ferrous Oxy Hydroxide) which along with the mother liquor is taken either to a pigmentreactor or a tank, with scrap basket for further neutralisation of acid.

If precipitation is carried out at 90°C in pigment reactor, with air oxidation at pH > 7, blackiron oxide pigment is obtained with a magnetic structure and reaction is stopped at Feo/F2O3 = 1:1.

The exit pigment slurry is filtered in a centrifuge, dried in a furnace and ground in a mill grinderand further dried in a barrel dryer. Total processing time can be 2–7 days. If yellow nuclei isproduced in pigment reactor, highly consistent yellow iron oxide pigment with pure colour can beobtained.

By slightly altered route and parameters, red iron oxide pigment can be made. If the picklingsolution contains other metallic ions in large quantities, this has to be removed to get bright colourpigments. This process, known as Peniron process, is widely used for yellow iron oxide.

C. (i) Calcination of α FeOOH with small quantities of magnesite compounds gives homogeneousbrown (FeMn)2O3 pigment.

(ii ) Brown pigment-Controlled oxidation of Fe3O4 at 500°C produces a single phase γ Fe2O3with a neutral brown hue.

(iii ) High quality iron oxide pigment, also called copperas reds, is made by thermal decompositionof FeSO47H2O in a multistage (3 stage) rotary dryer used for calcining which produces α Fe2O3.The α Fe2O3 is transferred from a tank filled with agitator and transported to a cyclone to removesoluble waste and red iron oxide is sent to dryer followed by grinding in pendular mills pin mills andjet mills depending on hardness accrued.

(iv) Orange iron oxide with (γ-FeOOH) is obtained if dil solution of Ferrous salt is precipitatedwith NaOH or other alkalies until almost neutral. The suspension is then heated for a short period,rapidly cooled and oxidised. The suspension is filtered, dried and ground in rotary mills.

(v) Very red iron oxide pigment, with pure red colour, may be obtained by first preparing αFe2O3 nuclei and continously adding of iron (II) salt with atmospheric oxygen addition at 80°C.Hydrolysis and neutralisation are carried out by adding NaOH and keeping pH constant. The rest ofthe process-filtration, drying and grinding are same as in other processes. Some neutral salts are alsoproduced as by products in the precipitation and hydrolysis process.

D. Properties of Iron Oxide PigmentsThe final products is same for all the processes, Fe+3 -α Fe2O3 but properties are dependent

on method of preparation. Thermal dehydration of yellow geothite gives lowest density product (4.5gm/cc).

The pigment value results from physical properties, determined by physical state (particle size,crystal structure, particle shape, agglomeration etc. The chemical properties involve composition,purity and solubility. The most important physical-optical aspect of pigments is its ability to colour

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SYNTHETIC IRON OXIDE PIGMENT 169

environment in which they are dispersed and make it opaque. The opacity of a pigment lies in itsability to prevent transmission of light which is applied. The yellow pigment size is 0.1–0.8 µm andrefractive index of 2.9–3.22.

The maximum dispersion of visible light occurs when pigment particle size range is 0.16–0.28µm. Red pigment has highest density of 5.2 gm/cc and size = 0.3–4 µm.

E. Test Lab Instruments(i) Sieve testing facility.

(ii ) Refractive index determination instrument.

(iii ) Atomic absorption spectro photo meter for crystal structure.

(iv) X-ray florescence analyser.

(v) Chemical analysis for composition and moisture determination.

Uses: In construction materials viz ceramics, cement, roofing granules, coating materials,plastics colouring, paper and magnetic recording.

Table 1International specification of iron oxide pigments

ISO ASTM DIN

Black Pigment 1248 D 769 ISO1248

Brown Pigment 1248 D 3722 ISO1248

FeO Content – D 3872 –

Red Oxide Pigment 1248 D 3721 55913T1

Yellow Pigment 1248 D 768 ISO1248

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22Chapter

DYES, INTERMEDIATES ANDDYEING

Dyes are complex organic compounds mostly soluble in water while some dyes are soluble indilute mineral acids. They are various types of dyes used for dyeing of textiles and yarns (naturalor synthetic), textile printing, colouring of plastics and other materials. Dyes are classified as under:

1. Basic Dyes–These are cationic dye mainly amino and substituted amino compounds, solublein acids only.

2. Acid direct dyes–Anionic dye used for dyeing protein based fibres-wool, silk, syntheticnylon and some types of polyacrylic fibres, applied from acid dye bath. These dyes are water soluble.Example–Chlorantine (ciba).

3. Azo dyes–Insoluble dye produced in-situ on fabric by coupling diazotised materials containingone or more azo groups–N : M–as chromosphore usually with hydroxyl/amino group/oxyquinonenitrosogr./Zanthene gr. or auxaphoromones gr. Example–Diamond black F. Many azo dyes werebanned both in India and abroad due to health hazards.

4. Reactive dyes–These dyes, under suitable conditions, recat to form a covalent bond betweenthe dye and cellulose fibres (cotton) and rayon. Example–chromazol.

5. Disperse dye–Forms finely divided solid solution with synthetic material fabrics/yarns viz.synthetic cellulose acetate, plastics and polyester. These dyes are substantially water insoluble.

6. Vat dyes–Water if soluble dye which are derivatives of anthraquinone or indigoid groups.These usually contain two keto groups which are manually applied to fibres from alkaline dye bothcontaining a reducing agent (sod. hdydro-sulphite). This process is called “Vatting” or “solublising”.Example–Victoria blue.

7. In-grain dyes–These are produced in situ on fibres when cotton impregnated with anilineand oxidised with an oxidising agent.

8. Vegetable dye–Naturally occurring colouring matter, containing organic dye. Example–Henna.

9. Solublised vat dyes–There are indigo dyes in acetic acid or ammonium sulphate solvent.

10. Mordant dyes–These dyes are those which receive a mordant (hydroxides or salts) to formcomplexes called “Lakes” resulting in satisfactory dyeing on fibres (substrate). Example–anthracenedye (alizarine).

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DYES, INTERMEDIATES AND DYEING 171

11. Food colours–These are nontoxic coal tar dyes suitable for adding in food products. Thesehave stringent standards for food colours. Products for exports to USA require FDA rules compliance.Eu standards to be followed for exports to Europe.

Dye IntermediatesThese are made from coal tar primary compounds viz Benzene, tolune, naphthalene, cresol,

anthracine, xylenes etc. Coal tar itself contains 200 aromotic compounds. The primary compoundsof coal tar are converted to dye intermediates by series of reactions like nitration, sulphonation, alkalifusion, reduction, chlorination, oxidation and condensation so as to form hydroxyl, amino and othergroups, introduced into the original hydrocarbon materials to form intermediates. Dyes are madefrom these intermediates.

Dyes are usually named by the dye compounds or patented name, given by reputed manufacturers.Germany is pioneer in making dyes.

Dyeing ProcessWater requirement–A high quality of soft water, having low hardness, is required in dyeing

process. The amount of water required varies for different materials to be dyed. For example 1 kgof cotton yarn will require about 5 gallons of water in dye vat. In case of wool the ratio is 1:14.For dyeing process, involving circulation of dyeing solution, water requirement is less, about 1:10.Post dyeing process required water for acid/alkali removal from substrate as well as final washingwith water.

The percentage of dyeing materials required is based on wt. of materials to be dyed (substrate)For example, in case of Acid dyeing on wool, usual % of dyeing materials required are:

(a) H2SO4–4%

(b) Glauber salt–20%

(c) Acid dye–X%

For colour fastness, often post washing with required chemical solution is required.

Dyeing EquipmentVarious equipment are required depending on process of dyeing of textiles materials. The

process can be manual, semi continuous or continuous.

Colour Index of DyesBasic information in given in colour index international (9 vols) and all dyes are given a C.I.

no. and also a general name. A difference of 5 in between two dyes. Colour wheel is given in Fig.1 in Chapter 32.

Banned DyesGermany has banned 20 azo dyes. India had banned some 65 acid, direct and disperse dyes

and 45 benzidine dyes.

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23Chapter

FLOURESCENT OR OPTICALWHITENING AGENT (FWA)

These are complex organic compounds soluble in water and is used to impart excellent whitenessyellowish tint of textiles is produced by absorption of short wave length ultraviolet light (violet toblue). Optical brighteners absorbs maximum UV light-in the wave length of 350–575 nm range andemit the absorbed energy in the blue fluorescent range, having maximum wave length of 415–495nm in the visible range. The material looks like dazzling white.

Most of the FWAs are derivatives of stilbene (common) or 4,4 diamino stilbene trizoles,oxazoles, imidazoles which are five members nitrocycles gr. often 6 members FWAs viz coumarinesare used. FWAs are different for particular textile viz cotton, polyester, paper pulp etc. For cottonand paper bleaching, suitable FWAs are bistrianzinyl and bisstyrylbiphenyl di-sodium salt. For polyesteruse. 4 methyl-N-methyl napthalamide can be considered. FWAs are arranged in a series starting fromFWA-1 to FWA-220 and are characterised by groups as R, R1, R2 R3, .......

Example: FWA R, Group

16 OCH3

21 – N(CH2CH2OH)226 – N(CH2CH2OH)2

22 – N O

Fluorescence effect of organic FWAs is the fraction of light energy that is absorbed andemitted; in fluorescence, concentration of whitening agent, to be used, varies from 0.002–0.2%.

Types of FWAs for use in bleaching of different materials

Material FWA FWA no.

1. Cotton Bistrianzinyl 70

2. Polyester 4 methoxyn 74

Methyl naphthalamide 75 and 52–55

3. Wool, Cellulose acetate- coumarins 67

rayon and polyamides 68 and 69

4. PVC and Synthetic fibres 14, 47, 70

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5. Paper pulp 21, 24, 26

6. Moderate washing temperature (tex.) 20, 22

7. PAN Fibres 50, 51, 52, 72, 73

Often some stabilising materials are required during bleaching. The toxicology of FWA usedmust be considered and LD-50 must be high (LD50 above 5000 mg/kg). Also environmental waterpollution must be considered and suitable water pollution treatment method must be utilised.

Uses of FWAsDetergent 50%, cotton, synthetic textiles (15%), plastics and paper pulp (30%), and for soaps

and biological staining.

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24Chapter

AFLAME RETARDANTS, HALONS,FIRE ALARMS/HYDRANTS AND

RUBBER AND EXPANDED PLASTICS

(I) FLAME RETARDANTS

1. Flame retardants are active chemicals (inorganic and organic) applied to fabrics, plastics andother materials for retarding flame generation when such coated fabrics or other base materialsget ignited due to some reason. The list of such chemicals are given below:

(i) Zinc borate, (ii ) Al hydroxide (iii ) Molybdenum carbonate (iv) Bromine compounds (v)Chlorinated alkanes (vi) Halogenated phosphate esters (vii) Aluminium oxide trihydrate (viii)Magnesium hydroxide (ix) Cyclo aliphatic compounds (x) Ferrocene and (xi) Antimony trioxide.

2. A flame retardant either inhibits or even supresses the combustion process and depending onthe nature of base material, a flame retardant can act physically or chemically in solid, liquidor gaseous phases. Flame retardants interfere with combustion during a particular stage ofprocess viz during heating, decomposition, ignition or spread of flame.

3. Physical action of flame retardants by way of:

(a) cooling-endothermic process triggered by a retardant e.g., Aluminium oxide trihydrate,

(b) protective layer formation-gas/solid protective layer e.g., halogenated phosphatic esters

(c) dilution-inert substance (fillers) and additives which arrest gases from decomposition and dilute the fuel e.g., Aluminium hydroxide.

4. Action of some flame retardants is base material specific viz Ferrocine in polyurethane; Aluminiumoxide trihydrate and Magnesium hydroxide do not generate smoke.

5. Application-After cleaning of fabric, a small portion of retardant chemical solution is sprayedover the fabric and allowed to dry slowly. Test is to be carried out after cooling to ascertainthe extent of flame retardation viz determination of oxygen index before and after applicationof retardant. In case of plastic with flame retardant, it is mixed with plastic during moulding

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stage and burning characteristics of treated plastic is determined and so also for the virginplastic. Halogenated flame retardants are also used in plastics.

Typical composition of a treated plastic is polycarbonate, 93% decarbomo diphenyl ether 5%and antimony trioxide, 1.9%.

6. Uses-electronic, electricals, toys, tents, carpets and drapers and children sleep ware etc.

(II) HALONSHalogenated Fire Extinguishing Chemicals

Halon is a trademark for tetra fluoro ethylene polymer. Halons are new fire extinguishingchemicals designated as 4 digit nos. The chemical compounds contain halogen atoms in addition tocarbon atoms:

(i) 1st digit indicates no. of carbon atoms

(ii ) 2nd digit indicates no. of flourine atoms

(iii ) 3rd digit indicates no. of chlorine atoms

(iv) 4th digit indicates no. of bromine atoms.

Types of Halons:

Remarks

(a) Halon 1001 (CH3Br)

(b) Halon 1211 (CBr C1 F2) Active agent 6%

(c) Halon 1301 (CF3Br) Active agent 5%

(d) Halon 2402 (C2F4Br2)

CharacteristicsHalons are efficient flame extinguishing chemicals which causes flame to sink and stay at the

base of the flame. It removes the active chemical species involved in chain reactions for flamepropagation. Halons are over two and a half times more active than CO2 and suitable for liquidcombustible materials fires. Halons are generally not used in solid combustible fires.

It is self extinguishing and inert to all chemicals and resistant to high and low temperature.

Toxicity: Except Halon 1301, rest are non toxic. Halon 1301 has TLV-TWA = 1000 ppm andMAC = 6100 mg/m3. Halon concentration above 10% is dangerous to human being.

Application: It is applied by portable fire extinguisher. Fixed installation should be unoccupied.Concentration upto 4% is tolerable for one minute only.

(III) FIRE DETECTION ALARMS

There are three methods of fire detection, (1) Ionisation detection chamber by α particles and(2) photo electric detection chamber by difference in photo voltaic cell e.m.f. and (3) fusible alloywater sprayers.

1. Ionisation Smoke Detection Chamber The process uses the principle of generating α particles from Radium or any other artificial

Radium isotope or ultra violet rays; α particles in the air (O2 and N2) molecules, thereby knocking

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out an electron from air molecules. The molecules, so hit, become ions and move to -vely chargedelectrons.

If air particles, containing smoke and dust, enter the chamber, the ionisation chamber conditionsis changed. The solid smoke particles will absorb α particles with the result that fewer no. ofparticles are now available for ionisation of air and the current passing through the circuit will bereduced, thereby triggering a connected alarm circuit. A cold cathode tube (CCT) is usually used forthe smoke alarm detection. The system is used in offices, shops etc.

CCT

CC

OP

OP = open ionisation chamberCC = closed ionisation chamberCCT = cold cathode tube

Fig. 1. Ionisation smoke detection circuit.

2. Photo Electric Cell for Smoke DetectionThe system uses a photo electric cell chamber with air inlet and outlet provision in between

light source and photo cell. Air, containing smoke and dust, while crossing the light to photo cell,changes the photo voltaic cell e.m.f. This triggers an alarm circuit due to reduced intensity of lightfrom light source as a result of smoke and dust in air. The system is used in offices, shops etc.and is less costlier than isotope based detector.

To alarm system

Photo cell

L ight source

Air

Fig. 2. Photo electric smoke detection system.

3. Fusible Alloy Water SprayersThe system is suitable for storages containing combustible materials. The system is a part of

a fire hydrant system and a fire water pipe line grid is placed over head in combustible storage. Thefusible plug sprayers are put in the firewater grid mouths having threaded connections for easyreplacement.

The fusible alloy melts due to heat, whenever there is a fire in the combustible material storagebelow, resulting in water at fire hydrant pressure is sprayed on the fire thus putting out the fire. Withthe fall in firehydrant pressure due to operation of water spraying system, an alarm circuit is alsotriggered. New fusible alloy sprayer nozzles are to be put once such sprayers are activated by fire.

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(IV) RUBBERS AND EXPANDED PLASTICSA. Natural Rubber

Available from 2 species, the Hevea brasili-ensis tree and Parthenium argentatun called guayutebush. Natural rubber crystillises at below 20°C.

Latex: pH = 6.5 – 7

Density = 0.98 gm/cc

Total solids = 30–40%

Rubber phase = 96% (wt. rubber)

Hydrocarbon = 1%

Protein = 3%

The field latex is processed by adding 0.4% ammonia and then centrifuged. After centrifugation,the cream rubber concentrate is raised to 1.6% ammonia (wt.).

B. Rubber blends are used in 75% for all elastomars. Heterogeneous blends of natural rubber, SRBor (cis-butadiene rubber-styrene) are used mainly in tyre treads as it reduces abrasion.Homogeneous blends of rubber are rarely used; such homogeneous blends are formed ifdifference in solubility parameters is smaller than 0.7.

C. Expanded or foamed plasticsThese are blends of plastics with air. They are classified according to cell structure, viscosity

and nature of parent plastics. Their uses are mainly for thermal insulation (ps foam) and flexiblefoams for damping and cushioning for packaging. Poly ethylene, Poly urethane, Polystyrene andPlasticised PVC are semi rigid to flexible foams. PS copolymer with acrylonitrile or maleie anhydridefoam has increased resistances to heat and solvent. Surface treatment of such foams with fireretardants (e.g. hexabromocyclodecane or pentabromo phenyl allyl ether) makes the foam flameproof (class B1-low combustible as per DIN 4102).

Modulus of elasticity of expanded plastics decreases approximetely proportional to their polymercontent. Tensile strength of Foamed plastics follows the law of simple mixing. The cell structurecould be open, closed or mixed. Open celled foams are always air filled, regardless of blowing orexpanding gases. Trapped gases in closed cell structure can be exchanged by surrounding air bydiffusion only through polymerisation. All plastics can be foamed either by air or N2 or chemicalblowing agents (Azo dicarbo amide, Hexamethylene tetramine).

D. Above glass transition temperature Tg 20°C or more elastomers exhibit rubber like behavior.The sheer moduli at this temperature range vary between approximetely 0.1 and 100 N/mm2

and exhibit a high visible deformability.

(V) FIRE HYDRANT SYSTEM

1. Every manufacturing and storage facility, large and medium, is to be provided with fire fightingfacilities as per statutory requirement. The designing of such a system by the approvedcompany is required as per requirement of the factory act as well as TAC requirements. Thisis essential for installation’s safety against hazards of fire. Fire insurer of the factory needs toknow whether the factory has a fire licence which is possible if the Fire installation is providedby a TAC approved co. TAC stand for Tariff Advisory Committee.

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2. A composite fire protection system of a factory usually consists of:

2.1 Underground fire hydrant system with loop design and isolation valve.

2.2 Overground fire hydrant system for different floors.

2.3 Hydrants water supply at 8 kg/cm2g press with strategic underground loop isolation valves.

2.4 Fire pumphouse with booster pump (constant running) = (1+1) electric driven and electricdriven fire pumps (1+1) plus a standby diesel operated pump with heavy duty battery withcharger, are usually provided. Water is from fire water reservoir.

2.5 Accessories for hydrant like standpost (4") with hose coupling. Fire hoses with hydrantcoupling, 3" nozzle, Pr. gauges tapping pt. at end points of hydrants. The fire water pump startswhenever pressure falls to below 7.5 kg/cm2g.

2.6 Foam maker is connected to Fire hydrant system for Foam-water spraying inside Fuel oilstorages as well as water sprinking on tank body.

2.7 A Fire station with a Fire water cum foam tender, Fire hooter alarm system, Remote fire alarmswitches at strategic plant stations to alart Fire station, Fire axes, portable fire extinguishers etc.are essential requirements for fire station.

2.8 Portable Fire extinguishers, compressed CO2, Soda-acid (CO2), Carbon tetra chloride, drypowder, and foam fire extinguishers are to be provided for any fire including electrical fires atstrategic locations of plant areas as per TAC requirement. Their nos. and capacity will alsoconform to TAC requirement. Trolley mounted compressed CO2 fire extinguishers can also beused. Foam and Halon fire extinguishers are also put into use. Sand buckets and empty bucketsfor water are also to be provided in plant areas.

2.9 Source of reserved water for fire hydrants–This can be a surface water reservour close to Firestation or an overhead fire water tank coupled with factory drinking water supply from ownW.T. Plant or outside water service provider. Often an overhead fire water tank is provided.

2.10 In addition, (i) the empty bags storage of the end product, if in bulk, is also provided withfusible alloy fire water spraying system with own alarm system and (ii) fire detection alarmsystems in offices/godowns. Packed goods storages are also provided with fire detection alarm.

3. Classes of fire has been given in Vol. II B, T-34.

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FLOAT GLASS, CARBON BLACK, ELECTROPHORESIS.... 179

Chapter

BFLOAT GLASS, CARBON BLACK,

ELECTROPHORESIS, DRY ICE ANDTECHNOLOGICAL DEVELOPMENT INIRON AND STEEL INDUSTRY ANDELECTROLYTIC CHLORINATOR

24

(I) FLOAT GLASS

1. Float glass is transparent, both sides are flat and parallel and polished so that a clear andundistorted vision and reflection is obtained. It was discovered in 80’s and process of manufactureperfected. The glass is made by floating on a heavier molten metal viz molten tin (having greaterdensity than glass).

2. Pilkington Float Glass Process of ManufactureThe charge raw materials for glass is melted in a glass furnace and conditioned by adding

sodium sillicate, arsenic/antimony trioxide. The melt glass is flown in a molten tin bath where a topglass layer, typically 9m wide 45m long of desired thickness floats over molten tin. The temperatureof molten tin bath falls in the working range of temperature of glass. Because of extreme goodsurface of molten tin, molten glass, as it flows over tin, smoothen sits surface and no furtherpolishing, smothening of glass surface is necessary. The glass body is rigid enough to travel withoutdamage, by the time it leaves the bath. Tin is used as a medium of floatation because of its surfacetension of 0.55 N/m and density 5–9 gm/cm3 compared with surface tention and 2.2–2.5 gm/cm3

density of glass. The m.p. of tin is only 505°K.

The float glass is of mirror quality and production capacity is more due to higher velocity whichis 5-10 times more than other float glass manufacturing process like Libbey-Owner’s process.Pilkington process requires 4 persons/shift for 100 MT/day plant. The glass melting bath capacityusually is 2 MT of melt per sq. mt per day. Heat input of 10,000 Kj/Kg of glass and temperature1948°K and cycle of heating 16–17 hrs. (initial slow heating).

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3. Uses of Float GlassMirrors, show cases, display windows, Glass doors etc.

(II) CARBON BLACKA. Surface Area

Grade Surface area (m2/gm)Coarse thermal black 10Fine Pigment grade 1000Tyre grade reinforcing 80–150Carbon Black

Carbon black having surface area of 150 m2/gm is of 1.0 nm pore dia. Furnace black CB has10–25 nm pore dia. and varies from 1–90 nm pore dia. depending on process used.

B. Density1.8-2.1 gm/cc. (Graphitation increases it) to 2.185.

C. Carbon black Feed Stock (Petroleum) specification (CBFC)

Flash point = 70°C minBoiling range = 200°C plus

BMC Index = 105–125(US Bureau of mines corelation index)

Pour point = 50°C (approximetely)Viscosity =

Temp. of solidfication =Alkaline Content =

Mid B.P =Sulphur content =2–4.5%

C

H ratio = 62–332

The CBFC usually consists of:Monocyclic aromatics = 10–15%

Bicyclic aromatics = 50–60%Tricyclic aromatics = 25–35%

Tetra cyclic aromatics = 5–10%Note: In India CBFC contains 4–4.5% sulphur which reduces the BMCF yield (BMCI = 82–83).

D. Composition of Carbon BlackCarbon = 80–95% wt.

Hydrogen = 0.3–1.3%Oxygen = 0.5–1.5%

Nitrogen = 0.1–0.7%Sulphur = 0.1–0.7%

E. Some grades of carbon black : N 220, N 330 and N 660.F. ASTM grades of carbon black are SAF, ISAF, HAF, FF. and FEF.

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G. Other Types of Carbon Black Raw Materials

Type Raw material

1. Channel black = NGor Gas black

2. Furnace black = Coal tar

3. Lamp black = CBFC

4. Tyre black = CBFC

5. Pigment grade = CBFC

6. Acetylene black = C2H2

There are two processes of manufacture of Carbon Black by incomplete combustion (Partialoxidation) and thermal Pyrolysis. Surface area of different carbon blacks varies depending on rawmaterials and process.

(III) SEPARATION OF MATERIALS BY ELECTROPHORESISThis is an advanced technique for separation of ores, plastics and resins, vermicullite-mica

rock, making iron ore superior concentrates and causing removal of silica from iron and chromate ores.

Electrophoresis is caused by applying electric field either from a high voltage DC source orfrom charged particles’s own field. The charging of particles could manifest in three forms viz. ionbombardment, conductive induction or contact charging.

For grannular ores/materials, these materials fall on a grounded roller and charged by coronadischarge placed above the roller surface. Both conductors and non-conductors in ores/materials thusbecome charged but only the conductor looses the charge on falling to grounded roller of the crusherin different heaps. Uniform electric field is produced by corona discharge. In the di-electrophoresapplication, catalyst fines from Petroleum products and fibres from food stuff (in air media) areseparated.

(IV) DRY ICEManufacture

CO2 gas from sources viz. brewery etc. is drawn through a blower and is subjected to waterwash to remove aldehydes, higher alcohols (amyl alcohol), glycerol, H2S etc. After washing, CO2gas is passed through a cooler and then through active carbon separator for removal of moistureand hydrocarbons if any. Two active carbon separators are used-one remains in line while the otherone is regenerated by live steaming of bed and water cooling tubes followed by air purging fromprevious use. The water cooler is embeded in active carbon separator for removing heat of separationby cooling water. Since pore diameter of active carbon is 0.3 nm and is less than the moleculardiameter of gases to be removed and the active carbon molecular sieve allows only CO2 gas, to passthrough as its molecular diameter is 0.28 nm only.

After first stage molecular separator, CO2 gas is further treated with Potassium Permaganetewash to remove organic matters which give bad smell. CO2 gas is then dried in a silica gel drier withhot air regeneration when moisture in CO2 gas is reduced to low dew point level, usually –50°C.After drying, CO2 gas is further passed through 2nd stage active carbon separator to remove lasttraces of moisture and impurities. In silica gel drying, regeneration temperature is 120–150°C and

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heat consumption per kg of water removed is 8000 Kj. In molecular sieve when moisture is removed,usually 12000 Kj/kg of heat is consummed (for 2 layer ms).

Extremely pure CO2 gas, thus produced from m.s. separator column, is then compressed to70–76 kg/cm2g, CO2 cooled in after cooler and chilled by refrigeration in chiller—when liquid CO2is produced. Liquid CO2 is then expanded to atmospheric pressure through nozzles in the chiller whensnow like dry CO2 is formed by its own refrigeration effect. 1/3 rd of CO2 is transformed into dryice and remaining cooled CO2 gas is recyled to CO2 compressor suction. The solid dry ice iscompressed in a hydraulic press and moulds of 12–100 kg blocks are usually made. By expandingliq. CO2 to ambient press, the temperature of CO2 falls below the tripple point of CO2 which is –56.5°C at 75.1 PSIA (518 Kpa). The heat of formation of dry ice is 573 Kj/kg.

From breweries

Raw C O gas2

Booster

Cooler

Active carbonms adsorber-1

Perm anganatewash tower

Hydrocarbon

Organic impurities

Moisture

Odorous impurities

Silica gel dryer

Active carbon msSeparator-2

CO compressor2

Cooler

Liq C O 2

Chiller

Expansion

Press

Rec

ycle

D ry ice blocks packing

Fig. 1. Block diagram for dry ice maufacture.

Uses of Dry IceIt is mainly used in food industry for the transportation of deep frozen products and laboratory

chilling or other uses.

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(V) TECHNOLOGICAL DEVELOPMENT IN IRON AND STEEL INDUSTRY1. Blast furnace

Japanese have developed artificial intelligence in determining internal reactions, resulting intemperature variation in a zone and overcoming this by correcting feed additions for uniformtemperature.

2. PCI (Pulverised Coal Injection) SystemBy injecting pulverized coal in B.F. coke requirement is reduced. By PCI technology, injecting

1 kg of coal, coke requirement comes down by 0.1 kg and corresponding coal requirement for cokeproduction reduce by 1.5 kg. Optimum PCI ratio is 100–105 kg of coal/ton of pig iron; lowgradecoal and iron ore can be used.

3. DIOS ProcessDirect iron ore smelting process (trial run NKK in 1993-94).

Here B.F. is in two section with production section at the top of smelting reduction section.No coke and only low grade coal and lower grade of iron ore, can be used.

Feed is given to bottom section from where it traverses to upper section where it is prereducedwith CO gases from bottom under fluidised condition. The prereduced iron ore falls to the bottomsection through central pipe when molten metal is produced and tapped.

4. Steel Making(i) Open Hearth process is gradually being phased out in Japan. It is only 15% in operation and

EAF with continuous casting and annealing is used thus saving in cost time and 10% reduction inmanpower has been achieved.

(ii ) Scrap charge melting is carried in furnace and refining with alloying materials in laddle. Bythis power consumption in furnace heating is reduced by 1/5th and production is increased by1/3rd. D.C. Arc furnace instead of A.C. induction furnace also saves power.

5. BOF (Basic Oxygen Furnace)

Here, CaO, lime powder is injected in tyre along with oxygen. The power consumption, in steelmaking, varies from 4.6 Gcal to and 8 Gcal/ton.

The main objective of the above development is saving in energy, process optimization for moreproductivity, computerised control operation and saving in manpower so as to reduce cost and timeof operation.

(VI) ELECTROLYTIC CHLORINATORChlorination by liquid chlorine injestion in circulating cooling water and drinking water are old

methods for disinfection. Modern method of chlorination is by electrolytic chlorinator which is fedby sodium hypochlorite solution at preset chlorine dose to water for different end uses which requiredisinfection. Chlorine kills bacteria and HClO reacts with enzyme.

The sodium hypochlorite solution is prepared in an electrolytic cell by the following reactionusing purified brine solution :

2Cl– → Cl2 + 2e (anode)

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Cl2 + H2O → HClO + H+ + Cl– (cathode)

HClO → ClO– + H+

hypochlorite

Cl2 + H2O → HOCl + HCl

ClO– then combines with Na+ ion to give sodium hypochlorite. The cell can be mono polar,bipolar or once through/recirculating.

The process consists of storing purified brine in a saturation tank from where saturated brineflows to brine circulation tank. The brine is then pumped to electrolyser cells assembly with arectifier. The outlet sodium hypochlorite is divided into two parts—one part goes to hypochloritestorage tank and the other goes to brine circulation tank. NaClO from storage tank is then taken tofeed points.

Beneficial Effects of Chlorine Apart from DisinfectionOdour control, reduces BOD, control sludge bulking and slime formation etc.

Uses of Electrolytic ChlorinatorDrinking water, swimming pool and cooling water disinfection, Hospital sterilisation, food and

beverages, brewery and bottling plants. NaOH plant, sea water pumping stations etc.

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25Chapter

CERAMIC COLOURINGMATERIALS

1. Industrial ceramic pigments are prepared by solid state reaction with minerals, suitable forparticular reactions. Whiteness or opacity is introduced into transparent ceramic materials, suchas glazes, by the addition of substances called opacifiers that will disperse in those materialsof glazes as discrete particles. There discrete particles scatter and reflect some incident light.The dispersed substances in glazes must have refractive index that differs appreciably fromclear ceramic materials i.e., glazes. The refractive index ND20, of ceramic materials (glazes) is1.5–1.6 and refractive index of opacifiers must be greater than that of glazes. In case of glazesviz. tin oxide (III) (ND20 = 2.04), Zirconia (ND20 = 2.4, Zircon (ND20 = 1.85), titania (ND20

= 2.5) and for anatase and titania-rutile ND20 = 2.7.

2. The glazes and other ceramic coatings in ceramic materials after application of glazes withopacifiers pigments are then fired in electric furnaces or hot blue gases at a temperature lessthan 1000°C. Usually % of opacifiers differs according to type of opacifiers. For example,finely ground Zircon (as opacifiers) is used at a concentration of 8–10% Zircon. The glazedporcelain will be colourless if no pigment is used.

When pastel colour is required in porcelain, opacifier, along with a compatible ceramic pigment,is added to the coating. The pigment chosen, should belong to the same opacifier group. Forexample, Zircon opacifier should be used with Zircon or Zirconia pigments. For black colour,Zinc or Cobalt free ceramic pigment is to be used.

3. COLOUR COMBINATION OF GLAZES3.1 Yellow Pigment

Three combinations are available for firing temperature, more than 1000°C viz. Zirconia-Vanadium yellow with Zirconium silicate (opacifier) and Tin oxide with vanadium yellow.

3.2 Pink or Purple PigmentChrome-alumina, Pink spinnel is free, from CaO and low concentration lead oxide or basic

oxide. Most stable pigment is Iron-Zircon combination.

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3.3 Gray PigmentDiluted black Pigment with white opacifier. Other combination is Tin based opacifier with Tin-

antimony carsilerite.

3.4 Green PigmentChromium is basic pigment but it has various limitations. Usually Zircon-Vanadium blue and

Zircon-presscodynrium yellow are used. For bright green colour two parts of yellow pigment andone part of blue pigment with Zircon (opacifier) are used.

Copper containing pigments with opacifier is not used for making food containing ceramicarticles and non food items are made at lower firing temperature.

3.5 Blue PigmentsCobalt-Al. oxide (CoAl2O4) or cobalt with SiO2 are used with Zircon based opacifiers.

3.6 Brown PigmentsZinc, nonchromite brown spinnel or tin oxide (spinnel), iron chromite brown spinnel or chromo-

iron manganese brown spinnel.

3.7 Red PigmentCadmium Sulphoselenide or mixture of cadmium sulphide and cad. selenide, in the ratio of 4:1

(orange), 1.7:1 (red) and 1.3:1 (deep red).

4. Segar cone no. and temperatures for firing of glazes is given in vol. IIA.

5. There are 19 spinnel class pigments, Zircon group has 3 pigments, Baddeyte and borategroups, each has one pigment, Phosphate group has 2 Pigments and Rutile/Cassiterite grouphave 12 pigments.

6. APPLICATION OF COLOURS ON CERAMIC MATERIALSThere are five ways (i) As an engrave on a raw body (ii ) as a body stain (iii ) as an under

glaze colour to a bisque body (iv) as a coloured glaze (Pigment, dispersed in glaze) and (v) as anover glaze already formed and fired glaze as an overcoat.

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26Chapter

GLASS FIBRES FOR INSULATIONAND OTHER USES

1. The mineral fibres or glass fibres consists of finely divided fibrous glass, highly dispersed withspecific area varying from 0.1–0.2 m2/gm. The fibre is oriented in longitudinal direction onlyand the fibre is isotropic in 3rd dimension. Its open-ended Pore system offers little resistanceto flow which forms the basis of its good accoustic and thermal insulation properties. Its LowThermal conductivity, is based on fibre diameter and bulk density. The material is unsuitablefor load bearing structure construction. The material is also called glass wool or mineral wooldue to its similarity with wool. Glass wool is generally used for hot insulation.

Table 1Thermal conductivity of mineral fibres

Thermal conductivitywm–1°K–1

Type Temp°C Unit

Glass Wool 100 0.07

Glass Wool 200 0.078

Rock Wool 100 0.053

Rock Wool 200 0.090

Spl. rock Wool 100 0.041

Spl. rock Wool 200 0.060

2. MATERIALS USED IN PRODUCTION(i) Glass Wool

Quartz sand, limestone, dolomite, phanolite, kernite feldspar, nephelime-senite, menite, baryteand ulexite. Other chemicals used are sodium carbonate, sodium sulphate, barium carbonate alongwith recycle glass and resin bonding material.

(ii ) Rock WoolSingle material with limestone as additive to increase maleability. Minerals of suitable composition,

such as basalt, rhydite etc. are used.

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(iii ) Slag WoolBlast furnace slag with limestone is used.

3. BROAD COMPOSITION OF MINERAL FIBRESVitreous fibre having dia, 3–6 µm = 90–99.8%

and length 3–10 cm.

Phenol formaldehyde resin modified with = 10% (max)UF or melamine formaldehyde

Aliphatic mineral material = 1% (max)

Emulsifiers (noniomic Polyethylene, xylene) = 0.2% (max)Polymethyl siloxanol =0.5%

4. Chemical composition of mineral wool various with the process used. There are three processesof manufacture viz. (A) Owen’s rock wool process (B) Rotary Process and (C) Centrifugalblowing process. Mineral wool is inert to organic solvents even at higher temperature water andaqueous solution attack glass surface and reduce resin bond. Chemically the fibres are composedof silicate glass. Slag wool and rock wool are soluble in acids and are easily attacked by acidflue gases.

Table 2Chemical analysis of mineral fibres

A. Glass wool B. Rock wool C. Slag wool

Process used Rotary Owen’s Process Centrifugal blowing

Limiting temperature 570°C 700°C 735°CSiO2 57.3% (wt.) 52.7% (wt.) 46.8% (wt.)Fe2O3 0.35 1.8 1.0Al2O3 3.6 8.0 10.2FeO 0.1 1.4 0.3TiO2 – 0.6 –ZrO2 4.0 – –MgO 4.0 4.0 2.3CaO 8.6 20.9 37.7BaO 1.7 – –Na2O 11.2 10.3 0.9K2O 1.7 0.6 0.6B2O3 5.0 – –F 2.3 – –MnO – – 0.3

5. PROCESS OF MANUFACTURE OF GLASS FIBRES(i) Melting tank, consisting of reqd. amounts of raw materials, is a cross fired recuperative-

regenerative furnace or 4 steped flame furnaces or electric melting furnaces. Gas or oil is used inthe furnaces whose capacity can be 3.5 t/m3. For rock wool, cupola furnace can be used with fuel,either coke, oil or gas.

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GLASS FIBRES FOR INSULATION AND OTHER USES 189

(ii ) Owen’s Process uses steam or compressed air for blowing.

(iii ) Rotary Process is a two step process suitable for soft and long filaments.

(iv) Centrifugal type blowing is used for slag wool manufacture.

6. GLASS WOOL AND ROCK WOOLGlass wool and rock wool (mineral wool) are highly dispersed systems of finely divided fibre

glass with specific surface area of 0.1–0.2 m2/gm; glass wool filament dia. is 5.5 µ; density, 15 kg/m3

and Thermal conductivity (glass wool) at 200°C = 0.078 Wm–1.°K–1. These are suitable for hotthermal insulation.

The mineral wool is having higher filament dia. and density of 6.5 µ and density = 30 kg/m3

respectively and its thermal conductivity at 200°C is 0.090. A special variety of rock wool hasfilament dia. of 5.0 µ; density = 100 kg/m3 and thermal conductivity (rock wool), at 200°C is 0.060Wm–1.°k–1.

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27Chapter

PLASTICS

1. These are synthetic long chain high mol wt. hydrocarbons and other groups formed bypolymerisation reactions viz. addition polymerisation and condensation polymerisation in presenceof some additives which improve the product quality. The hydrocarbon material, which ispolymerised, is called monomer. Addition polymerisation or free radical addition polymerisationyields a polymer product of high mol. wt. The condensation polymerisation or ionic polymerisationis a combination of monomers with elimination of simple molecules viz. H2O or methanol orothers. Linear polymer are having short chain molecules and no branch chains and as such,molecular wt. of these polymer is lesser. Molecular wt. of plastics varies from 10000 to 100000or more. Plastics polymers, prior to curing (heating process), is called resins. Monomers oftwo different types when polymerise gives condensation polymers viz Styrene acrylonitrile(SAN) Acrylic Butadiene Styrene (ABS).

2. There are two types of plastics: Thermoplastics and Thermosetting plastics

Thermoplastics can be melted repeatedly without loss of mechanical or physical properties andreformed.

ThermoplasticsPolyvinyl Chloride (PVC)

Polyvinyl Acetate (PVA)

Polyethylene or polythene, PE (Low density and high density)

Polypropylene (PP)

Polystyrene (PS)

Polyvinyl Alcohol (PVA)

Polymethyl methacrylate (PMMA)

Cellulose Acetate (CA) polymer

Cellulose Nitrate (Celluloid) polymer

Polyacrylo nitrile (PAN)

Polycarbonate (PC)

Polybutadiene (PB)

Styrene acrilonitrile (SAN) and PTFE

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PLASTICS 191

Thermosetting PlasticsThese plastics are formed from certain virgin plastics by heating and cooling process which

cannot be remelted and reformed as it sets to a permanent form on cooling. On reheating it is likelyto decompose or deform.

Examples:

Melamine formaldehyde resin

Polyethylene terepthalate (PET)

Phenol and Urea formaldehyde (PF/UF)

Polyurethane (PUR)

Polymer silicones

Polyall (alkyd resin polymer)

XLPE (Polyethylene cross linked)

Acrylic resin

ABC

Nylon–6, Nylon–66

Polyester resin (Poly condensation of dicarboxylic acid with dihydroxy alcohols)

Furan

Acetal (Polymer of formaldehyde)

Epoxy resin

In addition to the above, there are other plastics, suitable for medical, scientific and industrial uses.

3. PROPERTIES OF PLASTICSThe properties are characterised by the following main physical and mechanical properties as

stated below:

Density and specific gravity. Plastics are generally solids with a few exceptions e.g., polysiliconeswhich are liquids.

Melting point, Vical softening point (°C) and Glass transition temperature, (°C), GTT givesability of a solid plastic material to crystallise and when relevant, indicates crystaline m.p. The abilityof a plastic to crystallise is determined by regulating its molecular structure. Usually GTT/Tg of manypolymers, except co-polymers is 2/3rd of crystalline m.p. In case of amorphous polymer, glasstransition will indicate whether or not the polymer is glass or rubber at a given temperature afterprocessing. Other properties are Tensile strength, Flexural strength, Modulus of elasticity, Impactstrength, Solvent Chemical, Electrical property (Die-electric constant), Water absorption rate and meltflow index. Plastics detoriate in heat and sunlight specially when there is no U.V. protection additives.

Virgin plastics are available in solid form (Pellets/granules); few plastics are in fluid form andpowder form.

4. ADDITIVESFor processing of plastics these are used to improve the quality, mechanical and electrical

property. Along with additives, some percentage of used plastics are added to the processingmaterials to improve melt properties. The additives are classified in several groups as under:

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(i) Fillers (Solids and reinforcement fillers e.g., talc in P.P., usual fillers and reinforcements are :Talc, Cellulose, Silica, Kaolin, Al(OH)3, Natural and precipitated carbonate, Carbon fibres, micapowder, glass fibres and spheres etc.

(ii ) Antioxidants–These are used to prevent degradation of plastics by chain breaking to preventoxidation and synthesis between antioxidants. Chemicals used are Tiophenols, alkylidene-bisphenols(300–600 mol. wt.) and alkyl phenols.

(iii ) Light (UV) stabilisers (UV radiation 360–380 nm wave length-to stop UV absorption fromsun light. Chemical used are Benzophenons, Nickel compounds, Cyanocinnamates, Salicylates, Benzoatesetc.)

(iv) PVC stabilisers–to prevent, detoriation by thermal stress. Chemicals used are Methylenemercaptide, Butylene carboxylate, Barium-Cadmium or Ca-Zn stabilisers.

(v) Plasticisers–These are high boiling organic compounds usually liquid which gives betterprocessing properties and imparts flexibility and stretch-ability of plastics/resin or elastomers.

(vi) Electron beam crosslinking of PVC gives higher m.p. PVC.

Thermal conductivity of plastics is low, usually 0.0004 cal-cm/°C.cm2.sec and linear thermalexpansion co-eff. of plastics varies from 30 – 70 × 10–6 m/m°C.

For PVC processing more plasticisers are required until brittle point is exceeded and propertieschange from rigid to soft. Type of plasticisers also depends on type of moulding-Injection, extrusionor blow moulding. Common plasticisers are Phthalates (Phthalic anhydride and isophthalic acid).Trimettileates, polyester, glutonic acid, acrylic acid, oleates, stearates, benzoates, terephthalic acidand hexanol etc.

(vi) Lubricants–added to improve viscosity of melt. Examples—Fatty alcohols, dicarboxylicacid esters, fatty acid esters of glycerol, fatty acid and fatty acid amines.

(vii) Cellulose derivities–used in coatings and adhesives.

(viii) Dye/pigment for colouring–generally azo/anthraquinone based dyes are used as pigmentsand metallic oxides and inorganic hydroxides are used in plastics including amorphous carbon. Sizeof pigments used varies from .01 to 1 µm.

(ix) Antistatic agent in plastic materials–High electrical charge develops into plastic materials dueto high volume and surface resistance and requires antistatic agent viz. cationic compounds, quaternaryalkyl carbonates and anionic compounds viz. alkyl sulphonate is to be added into the charge. Surfaceresistance of a plastic should not be more than 106 ohm. To provide earthing to atmosphere fromprocessing room, so as to prevent static electricity flash.

5. PLASTIC PROCESSINGThe virgin plastic moulding material usually in pellet form is mixed with required additives in

proper quantities in a Banbury mixer. The mixer is then throughly mixed and plastic processing isdone at above the crystalline melting point or in case of amorphous (powder) polymers above itsglass transition temperature. The charge is melted electrically and then led into the kneaders or rollersmaintained at 150–210°C and the melt is taken to moulds for the desired product.

In case of sheets/film products, film/sheeting machines are used. For cast films, celluloseacetate is used.

Various types of plastics are used in packaging industry. The list of different plastics forms,types and polymers used are given below:

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PLASTICS 193

Forms Types Polymers

Films Blown films Polyolefins, PVC, PET

nylon and EVA

Cast films PP, PS, PET and nylon

Coextruded films Polyolefins, nylon

Oriented films PP

BOPP PS, PP, PET

Strings for sacks LLDPE, HDPE, PP

Lamination Extrusion lamination

on paper/Al foil Polyolefins

Dry bond lamination PET, BOPP, MET

Injection blow moulding Containers, bottles PS, PVC, Polyolefins

(stretched) PET, SAN, PP

Multilayer bottles Polefins, EVOH

Injection moulded Containers PS, PP, HDPE

Transparent Containers HDPE, MMA

Closures PS, LDPE, HDPE, PP, ABS

Foamed Sheets and casting PS, Polyurethane

NB. EVOH is ethylene vinyl alcohol. Compression moulding is no longer used now. Foodproducts packages are generally irradiated at 1.5 mega rads.

6. OUT LINES OF SOME PLASTIC MANUFACTURE ROUTES(i) Ethylene → Ethylene Benzene → Styrene → Polystyrene

(ii ) Ethylene → dichloroethylene → Vinyl Chloride → PVC

(iii ) Ethylene → LLDP/HDP

(iv) Propylene → Cumane → Phenol → nylon

(v) Propylene → Isopropyl alcohol → Acetone → Acrylics

(vi) Propylene → Polypropylene

(vii ) Acetone → Acetic anhydride → cellulose acetate

7. FOAMED PLASTICS OR EXPANDED PLASTICSFoamed polystyrene, polyurethane and polyethylene are common plastics used in insulation,

packaging/lining of shoes soles etc. Process of manufactures involves in heating the polymer inpresence of additives and blowing agent, followed by cooling of the reactor effluent and finallypouring the effluent into the mould. Blowing agent is different for different polymers.

8. PLASTICS FABRICATION MACHINERIES(i) Injection moulding machine

(ii ) Injection blow moulding machine

(iii ) Extrusion machine

(iv) Film making machine

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(v) Cast sheeting machine

(vi) Lamination machine

(vii ) Sacks making machine on flat/circular looms.

9. PLASTICS FOR PACKAGINGThe following plastics resins or polymers are used in packing industries:

PVC, PET, BOPP (Biaxially oriented polypropylene), PP, PE (Low and high density), PS, SAN,LAN, PAN, EVA (Ethylene Vinyl acetate), EVOH (Ethylene Vinyl Alcohol), EMA and Foamed plasticsetc.

10. PROCESSES FOR PE MANUFACTURE(i) H.P. process

(ii ) Zieglar process

(iii ) Philips process

(iv) Standard oil process

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28Chapter

FLOCCULATION

Flocculants are chemical additives for flocculation, used in the separation of suspended particlesin slurry or fluid by agglomeration and thereby help settling. Flocculants are used generally forbeneficiation of ores, purification of water etc.

A. INORGANIC FLOCCULANTSAlum (Ferric alum, Pot. alum etc.) Poly Al. chloride, Sod. Aluminate, Ferric chloride, Ferrous

sulphate, Ferric sulphate and Sodium silicate.

About 10% solutions are used for inorganic flocculants.

B. ORGANIC FLOCCULANTSBasically these flocculants are cationic, anionic or amphoteric polymer compounds (mainly

polyacrylamides) of high molecular wt. For neutral suspension of fluid/slurry, anionic or nonionicorganic flocculants are excellent when the slurry contains inorganic solids. The cationic flocculantsare the best for neutral suspensions, containing more organic solids. Most of the organic flocculantsare available in company trade names, some of which are given below:

Trade name Manufacturer

1. Superfloc, Accurac — Amer cyanamid (USA)

2. Calgon, Hydraid — Calgon (USA)

3. Separen, Purifloc — Dow chemicals (USA)

4. Herobloc, Reten — Hercules (USA)

5. Nelco — Nelco chemicals (USA)

6. Polyfloc, Betz — Betz Laboratory (USA)

7. Sedipar, Polymin — BASF (FRG)

8. Magnafloc, Percol, Zetag — Allied chemicals (UK)

9. Praestol — Chemische Fabrik Stockhausen (FRG)

10. Kurifloc — Kurita Kogya (Japan)

11. Di aclear — Mitsubishi chemicals (Japan)

12. Sanpoly — Sankyo chemicals (Japan)

13. Sanfloc — Sanyo chemicals (Japan)

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14. Rohafloc — Rohm (FRG)

15. Floerger — Soe Nationale de Flocculant (France)

Tests Required for FlocculantsSedimentation test, Filter Plate test, Buchner funnel test, press. filter test, Determination of

filtration rate etc.

INDUSTRYWISE USE OF FLOCCULANTS

Industry Uses and type of flocculant used

1. Ores beneficiation Floatation process, thickening and filtrationof concentrates etc. Flocculant used iscopolymer of acrylamide and sod. acrylate.

2. Potash mining Classification of Potash solns, dewatering oftailings. Flocculant is same as in 1.

3. Barytes and Flourites mining Separation of floatation tailings. Flocculant,same as in 1.

4. Phosphate mining etc. Water recovery in mines, filtration, Gypsumfiltration, Phosphoric acid clarification etc.,Flocculant used in poly acrylamide and whichis used as in 1.

5. Salt works Classification of raw brines and sludgedewatering. Flocculant used is poly sod.acrylate and as used in 1.

6. Kaolin mining Thickening of Kaolin slurries. Flocculant usedis same as in 1.

7. Coal mining/washery Clarification of wash water, floatation tailingsand filtration of concentrated tailings andfiltration/dewatering of tailings. Flocculantsused as in 1, Polyacrylamide andPolyethylamine.

8. Bauxite beneficiation Thickening of redmud from Bayer process.Flocculant used is poly Sod. Acrylate.

9. Paper industry Dewatering of slurries and retention of Kaolinon paper machinery, clarification anddewatering of pulp recovery effluents.Flocculants used are polyethylamine, Polyacrylene polymer, copolymer of acrylamideand cationic substituted methacrylates.(neutralised and quaternised)

10. TiO2 Manufacture Clarification of black liquor and filtration ofTiO2. Flocculants used as polyacrylamide,last flocculant in Sr. 8 and cationic carbonylpolymers.

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11. Uranium manufacture Filtration of alkaline or acidic solns. Flocculantused are polyacrylamide and polyethyleneoxide

12. Sugar processing Clarification of sugar juice and dewatering ofsludge. Flocculant used is same as in 1.

13. Steel works, foundries Clarification of BF gas scrubbing water,clarification of effluents from sintering andpickling plants, clarification of electrolyticeffluents and purification of electrolytic solns.Flocculants used is same as in 1.

14. Bio-technology field Dewatering of biological slurries. Flocculantsused are same as in 8.

15. Water treatment plants Thickening of activated sewage sludge,effluent purification, floatation of activatedsewage sludge, phosphate precipitation andmechanical dewatering of sewage sludge.Flocculants used is inorganic flocculant,copolymer of acrylamide and sod. acrylate,polyacrylamide.

16. Potable water works Flocculation of surface water, clarification ofwash water of filters and filter conditioning.Flocculants used are inorganic flocculants,copolymer of acrylamide and sodium acrylate,polyalkalyne polymer and polyethylamine.

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29Chapter

PHOSPHORIC ACID

Phosphoric acid is a key material for the manufacture of other phosphatic and N.P.K fertilizersor N.P. fertilizers. These are mono ammonium phosphate MAP (N = 11%, P2O5 = 52% wt),Diammonium Phosphate (N = 18%, P2O5 = 46%), triple superphosphate (P2O5 = 46%) etc. Withaddition of Muriate of potash, KCl, N.P.K. grades are manufactured. About 85% phosphatic fertiliserare made form wet process phosphoric acid.

Commercial wet process phosphoric acid is classified according to the hydrate form in whichCalcium Sulphate crystallizes:

Hemihydrate – CaSO4.1/2H2O

Dihydrate – CaSO4.2H2O

The process is called wet because conc. sulphuric acid is used to digest the rock phosphateores. By 1980, hemihydrate and improved dihydrate processes were developed and 30–50% P2O5wet process phosphoric acid plant, upto 1300 Mt/day, came up.

The other dry process or electric furnace process of Phosphoric acid manufacture is anefficient process originally came up in 1935. But its use has declined except for the purpose ofmanufacture of elemental phosphorous or the acid as an intermediate for making phosphorous element.

Rock Phosphate Ores

These are of various types e.g., fluorapatite, Ca10F2(PO4)6, Chlorapatite 3Ca3(PO4)2CaCl2 andPhosphorite. Rock phosphate is characterized by BPL (Bone Phosphate of lime) value.

Chemical reaction

When a pure rock phosphate ore, say fluropatite, is reacted with sulphuric acid, the followingreaction takes place. There are various other reactions, as rock phosphate ores generally containvarious other impurities. For simplicity they are not shown below:

Ca10F2(PO4)6 + 10H2SO4 + 10nH2O → 10CaSO4nH2O + nH3PO4 + HF

where n = 0, 1/2 or 2, depending on hydrate form in which Calcium Sulphate crystallizes. Thereaction is the net result of two stages reaction. In the 1st stage, phosphoric acid reacts withmonoclacium phosphate and in the 2nd stage monocalcium phosphate reacts with sulphuric acid toform phosphoric acid. The two reactions take place in a single reaction.

The impurities in rock phosphate as well as in sulphuric acid, precipitate in many side reactions.Most rock phosphates have a higher CaO : P2O5 ratio than fluorapatite. The additional CaO consumes

198

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PHOSPHORIC ACID 199

more sulphuric acid and forms more calcium sulphate. The HF formed reacts with silica and othermore complex compounds. A variable amount of fluorine is volatilized as SiF4, HF or both. Theamount volatilized and the form it does so depend on phosphate rock composition and processconditions. Numerous side reaction compounds, some complex are formed in the reaction shownabove.

The heat of reaction, when n = 2 (dihydrate process), is calculated to be 230 or 257 kilo cal/gm mole of apatite. If the reactants enter the reactor at 25°C and products leave at 82°C, some heatof reaction is carried out with the reactants, the net heat to be dissipitated is 403 kilo cal/gm moleif 100% sulphuric used. In case of other acid concentration excess heat dissipitated is:

Sulphuric acid Heat dissipitation

98% 385 kilo cal/gm mole

93 329 kilo cal/gm mole

75 180 kilo cal/gm mole

Table 1Analysis of Florida Rock Phosphate

Constituent % by wt. Range Median

P2O5 29–38 32

CaO 46–54 51

SiO2 0.2–8.7 3

Al2O3 + Fe2O3 0.4–3.4 1.4

MgO 0.1–0.8 0.2

Na2O 0.1–0.8 0.5

CO2 0.2–7.5 4.5

F 2.2–4.0 3.7

Cl upto 2.9 1.0

CaO : P2O5 ratio (wt.) 1.35–1.7 1.5

Organic carbon 0.005–1.7 0.3

Recommended quality of R.P. should be as per median analysis.

1. Bulk density (Florida R.P.) = 136.157 Kg/m3

2. Source of R.P. are : USA (Florida and Tennessee Valley), Israel, Jordan, Algiers, andMorocco. Indian Udaipur R.P. quality is poor as it contains about 10% silica.

Dihydrate ProcessThis process is widely used because it is relatively simple and adaptable to wide range of grades

and types of rock phosphate ores and gives 26–32% P2O5 conc. of phosphoric acid with reactionat 70–85°C. The separation stage after reactor, is only one (filtration stage to remove gypsum or bycentrifuging).

Assuming 94% overall P2O5 recovery, the number of tons of rock phosphate required per tonof P2O5 required as Phosphoric acid is as follows:

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Table 2

Type Grade of rock Rock required in% P2O5 Tons/ton of P2O5

in acid

Low 29 3.67

Medium 33 3.22

High 38 2.80

Selection of Rock Phosphate OresGenerally Phosphoric acid plants are designed on the basis of some standard rock phosphate.

However, it is better to consider the use of rock phosphate from other countries, having slightlydifferent specification and to design plant facilities accordingly should it be found necessary to userock phosphate from other countries to avail of opportunities of competitive rates or to avoiddisruption to supply due to hostility or non-availability. The extra investment will be more than tocompensate for savings due to freedom of choice.

The extra facilities required in such cases are:

1. Additional grinding facility for harder rock

2. Extra filtration capacity

3. Slurry handling systems that can cope up with acid insoluble impurities in rock

4. More corrosion resistant materials for rocks that have corrosive impurities.

Complete chemical and mineralogical analysis of rock phosphate and trial run for selecting rockphosphate or changing the source, are required.

Factors to be considered selecting rock phosphate:

(i) R.P. to contain min. 32% phosphate as P2O5 for 16% W.S. P2O5

(ii ) BPL values of 68–72% and H2SO4 usually 98% at calculated amount

(iii ) Presence of impurities viz. iron pyrites, Al silicates and various fluorides within limits

(iv) Non Fluorides, iron, organic matter, Al silicates gives poor quality product

(v) Acid consumption is more if more Al and iron are present.

Sulphuric Acid RequirementIt can be determined from R.P. analysis. The followings are the typical parameters:

High Medium Low

CaO : P2O5 ratio in rock 1.70 1.50 1.35

H2SO4 reqd., ton/ton of P2O5 3.15 2.78 2.50

Receiving and Storage1. Rapid unloading and delivery system of R.P.

2. Less loss of R.P.

3. Easy storage with ability to separate shipment of supply storage

4. Efficient retrieval from storage

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PHOSPHORIC ACID 201

5. Storage covering against rain, dust and wind

6. Provision for expansion

7. Storage capacity should be one and half times the shipment capacity of tankers.

Rock GrindingDry grinding is used in older plants and some new plants, suitable for multi compartment

digesters. Prayon require 60%-200 mesh (Taylor) or 0.074 mm opening. Other new plants require25%-200 mesh, 60%-100 mesh, all minus 35 mesh. Ring roller mills often used with air classification.The power requirement depends on rock size, hardness and fineness is about 12–20 Kw per ton ofR.P. including air classification in bag type filters with a automatic shaking. Softer rock requires2/3–1/2 of the above value. But dust pollution is frequent due to leakage from pneumatic conveying.

Wet grinding is generally found in plants located near R.P. mine. It is done in ball mills. A slurrycontaining 62 to 70% solids is produced and fed to the digestors via a surge tanks. Power consumptionis lesser, 11–12 Kw/ton and there is no dust problem. For open circuit wet grinding the powerrequirement is 18 KWH/ton. The major disadvantages are, faster erosion of balls and liners of mills,decrease in amount of recycling water that can be used elsewhere in the plant and close control ofwater/solid ratio in grinding.

Calcinating of Rock PhosphateIt is a part of ore beneficiation process, often found necessary to eliminate high organic matter

content or decreased carbonate content or both. For organic matter removal, fluidized kiln at 830°Cis sufficient. The organic matter in R.P. also form part of fuel cost. Calcined R.P. also enhancesproduction of R.P. by 30–40% and saves antifoaming reagent in digester.

Reaction in DigestorsThere are several types of reactions vessels designed by manufacturers. The most important

factor is production of gypsum crystal of such shape and size which will allow rapid filtration ofslurry from digestor.

The losses of P2O5 due to lower recovery of P2O5 are:

1. Unreacted rock

2. P2O5 crystalises with gypsum through isomorphic substitution of HPO4 for SO4

3. Phosphoric acid lost in the gypsum due to incomplete washing

4. Others are spillage, leakages, washing of filter cloth, piping, equipment, scale removal andlosses as sludge.

Digester or ReactorA multicomponent reaction vessel is used having agitators. Sulphuric acid is poured with

recycled of weak phosphoric acid and discharged into 1st, 2nd or 3rd compartment (no. ofcompartment depends on plant capacity) as reaction system is designed not to mix R.P. and sulphuricacid directly to ensure slow growth of gypsum crystal to a relatively longer size for ease of filtration.Retention time of reactors varies from 15 hrs. to 3 minutes and usually it is 1.5 hrs. to 12 hrs. ormore. Also, a high concentration of free H2SO4 will result in the coating of R.P. with CaSO4 reactionproduct, thus blocking further reaction. A serious block in reaction systems can take hours or evendays to rectify.

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The rock slurry from wet grinding is discharged into 1st, 2nd or 3rd compartment or dividedamong them. The reaction temperature varies from 85–100°C. A portion of rock slurry is withdrawnfor temperature control and fed to a vacuum flash cooler. Part of cool slurry is fed to attack systemand part to digestor. The slurry moves from last compartment to first compartment. The digestortanks permit completion of reaction and lowering of any super saturation under mild agitation. Asmall adjustment can be made by adding small R.P. or sulphuric acid as required.

Premixing recycle weak phosphoric acid with conc. H2SO4, evolves much heat and vapoursof H.F., SiF4 which is also carried out, separately in some in plant in flash vacuum cooler to separateH.F. and SiF4 which can be used to produce hydroflourosilicic acid.

In Swenson Gulf isothermal process, a Swenson crystalliser is used as single reactor suitablefor granules of R.P. (0.42–1.1 mm or smaller) where such R.P. can be used with lower operatingand m/ce cost and control of atmospheric pollution.

A thin spray of conc. H2SO4 acid is sprayed on top of slurry while R.P., mixed with weakP2O5, is fed from bottom; an agitator agitates reactor fluid so that isothermal condition is maintained.The reactor slurry is filtered; waste and weak acid is recycled. Reactor cooling is by flash cooling.Such plants can be built up upto 650 MT per day.

In Rhone poulene process, temperature of reactor is controlled by flow of air on surface ofreactor by evaporative cooling of droplets of slurry picked up by a sprayer system. Sulphuric acidis also added as a spray at top of reactor. R.P is introduced through center at top zone of maximumagitation. The process is suitable for 100–80 MT per day P2O5. There are other processes usingsingle or multiple reactors.

Process Key ParametersControl of H2SO4 content in liquid phase is very important for close control of reactions, an

optimal values of 1.5% is typical and is difficult to control when reaction time is sort. Most of theprocesses used 8 hours reaction time with Kellog-Lopker dihydrate process (used in England) whichrequires a short residence time of 1.5 hrs. with two reactors but uses a automatic SO4 controlinstrument for close control of sulphate.

Table 3

Crystal form (s) No. of separation Conc. of product Temp. of Recrystallisationstages acid % P2O5 reactor temp.

Hemihydrate 1 40–50 85–100 –

Hemihydrate- 1 26–30 90–100 50–60dihydrate

Hemihydrate- 2 40–50 90–100 50–65dihydrate

Dihydrate- 2 35–38 65–70 90–100hemihydrate

Hemihydrate ProcessIn hemihydrate process of phosphoric acid manufacture, a high conc. of acid is obtained, until

that acid may not be further concentrated. Such consideration will depend on whether waste heatsteam from on site sulphuric acid plant can be used elsewhere in the plant. When concentration isnot necessary, both capital and operating cost become less. Product phosphoric acid is also somewhatsludge free and less aluminium in acid. However, better material of construction is required in reactor,pump, filtration, centrifuging as reaction temp. is high which enhances corrosion.

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PHOSPHORIC ACID 203

Hemihydrate-Dihydrate ProcessThis process, as developed by Nissan Japan and named Nissan H Process, uses only one

filtration process and gives pure by-product gypsum which can be used in other products ofmanufacture without any further treatment. The P2O5 recovery from R.P. is 2-3% or more as lossesof P2O5 in gypsum is very less. However the plant cost is higher due to elaborate process stream.Hemihydrate-Dihydrate Process with two stage filtration of centrifuging is also provided by FisonsHDH Process and Nissan C Process. However, extra capital cost, due to additional filtration stage,is offset by additional recovery of P2O5.

Filtration of Digestor EffluentThe effluent from digestor or reactor is filtered to remove gypsum and any insoluble materials

from rock phosphate or formed in the reaction from phosphoric acid completely and efficiently bycontinuous filtration, usually rotary tilting pan type filters, travelling pan filters, horizontal table filtersand even belt filters are used. The cycle of filtration in these filters proceeds as follows:

(a) Deposition of phosphoric acid–gypsum slurry on filter cloth

(b) Collection of phosphoric acid from filter by application of vacuum

(c) Two-Three counter current washers to completely remove the phosphoric acid fromgypsum and from filter cloth

(d) Discharge of washed gypsum

(e) Washing of filter cloth to prevent scale formation.

In the washing stage, successively weaker solution of phosphoric acid is collected. The lastwash is with fresh water or sump water. Very weak phosphoric acid, collected from last section,is returned to the preceding section. The filtrate from the first section is often returned to thereactors. In addition, some portion of product acid is also recycled to reactor to control percentagesolids at 40–50% level. The design filtration rate is 6.5 t/m2/day. The filtration rate varies due tovarious factors; type of R.P. and impurities including presence of insoluble matters like clay, use ofcrystals shape modifiers in reactors, control of reaction conditions viz. temp., conc. and viscosityof acid and extent of recovery. Filtration rate also varies due to design of filter, % vacuum, type ofcloth and other criteria.

Concentration and Clarification of Phosphoric AcidDihydrate Process Phosphoric Acid has a concentration of 26–32% P2O5. This acid can be

used in manufacture of some phosphatic fertilisers but for most other purposes, it is economicallypreferable to concentrate it by evaporation. The concentration of P2O5 for phosphatic fertilisers andother uses as below.

Table 4

Product Phosphoric acid conc. % P2O5

MAP (depending on process) 40–54

DAP 40

Shipment grade 54–60

Superphosphoric acid for shipment 69–72for fertiliser production

TSP–Den Process 50–54

TSP–Slurry Process 38–40

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Precipitates formed in phosphoric acid during or after conc. are usually collected at bottom ofcontainer. The precipitates formed before conc. are mainly calcium sulphates and fluorosilicates.Accordingly to acid conc. a no. of precipitates can be formed during and after conc. Theseprecipitates are called sludges and cause problems in handling and use of the acid.

Phosphoric acid concentrators may by termed as indirectly heated concentrators or directlyheated ones (uses are declining due to difficulties of recovery of phosphoric acid mist and fluorinecompounds from exhaust gases). Super phosphoric acid is made by concentration of 54% P2O5 acidin directly fired concentrator. Prayon, Nordac and others have developed acid concentrators from30% to 54% P2O5. Fuel requirement for this range of conc. is 140,000 Kcal/t P2O5 and power 70Kwh/t P2O5. Any liquid or gaseous fuel can be used. For conc. from 54% to 70% P2O5, fuel requiredis 600,000-800,000 Kcal/t P2O5.

Indirect heated concentrators are heated by steam or some heating media viz. dowtherm heatedby flue gases from a furnace in an exchanger. Common type of evaporators or concentrators withforced circulation or evaporator-crystalliser, where precipitates grow into coarse crystals and removedby centrifugation or settling. For conc. from 30% to 54% P2O5. It can be carried out in 1, 2 or3 stages. Steam required for conc. is 1.90 t/t P2O5, power 11–16 Kwh/t P2O5 and cooling water 6m3/t P2O5 for condensers. Fluorine removed during conc. is about 70–80% of original conc. in acid,most of it is volatilized or condensed in condenser and recovered.

For conc. from 54% to 70% P2O5, H.P. steam (27 ata 230°C), required is 1 ton per t P2O5,power, 24 KWh/t. Fuel for downtherm heating is 640,000 Kcal/t P2O5. In concentrating Phosphoricacid to super phosphoric acid 69%–72% P2O5, most of fluorine is volatilized so that F content isreduced to 0.2–0.3%. Reactive silica is added during conc. to enhance fluorine evaporation and Fcan be brought to 0.1%. Such acid is suitable to produce dicalcium phosphate or ammoniumphosphate, used for animal feed also.

Advantage of Super Phosphoric Acid:

1. Saving in freight cost

2. Sludge elimination

3. Acid is less corrosive

4. Suitable for production of clear liquid fertiliser (ammonium polyphosphate solution).

5. The acid can be used to produce compound fertilisers by melting route.

The main disadvantages are higher energy requirement, high viscosity (acid required heatingupto 60°C prior to pumping) and corrosion in concentrator.

Table 5Chemical composition or Super Phosphoric Acid

Phosphoric acid, as P2O5 = 69–72%

Fluoride as F = 0.2–0.3

When reactive silica is added during concentration of Phosphoric acid, F content can bebrought down to 0.1%.

Uses: For dicalcium phosphate production, ammonium phosphate.

Use of Sludge in Phosphoric AcidPrecipitated sludge in phosphoric acid contains about 38 (Max) distinct Phosphate compounds

depending on impurities present in rock and sulphuric acid. The precipitates appear before, during

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PHOSPHORIC ACID 205

and after conc. Precipitation is a continuous process in storage of phosphoric acid. The usual methodof separation of precipitates is by centrifuging/filtration. Sludge formed after conc., contains a highproportion of complex Al and Fe phosphate compounds e.g., (Al, Fe)3KH14PO4)184H2O. The separatedsludge is mostly citrate soluble and is often used in T.S.P. Production where TSP is sold on the basisof citrate solubility and not water solubility basis. The sludge can be mixed in the production ofnongranular MAP which is used as an intermediate for the production of compound NPK fertiliser.

Material of ConstructionReaction tanks/ reactors and its agitators are subjected to most severe corrosive action. The

tanks are often made up of lined steel tanks or concrete with carbon brick lining inside. Suitableconcrete mixture with additives are used in case there is carbon brick lining damage. The flashcoolers and circulating pumps as well as filters are subjected to severe corrosion. Abrason is mostprominent in vessels starting from reaction to filtration steps. The quantitative value of corrosion isthe result of chemical and physical factors. The presence of impurities in phosphoric acid enhancescorrosion.

1. Physical FactorsPeripherical speed of process fluids;

The speed, usually considered in a phosphoric acid plant is given below

Filter cell = 30 m/min

Pipes = 60 m/min

Agitators = 250 – m/min

Pump impeller = 1000–1500 m/min

2. TemperatureAlthough temperature level is lower, corrosion gets enhanced with rising temperature.

3. Chemical Factors(i) Conc. sulphuric acid in presence of metal cations, Ca++, Al++, Fe++, etc.

(ii ) Excess H2SO4 – this causes more corrosion if excess is more than 1.5–2% or H2SO4 conc.is beyond 20 gm per lit. in reaction mixture. Pitting, due to chlorides, is enhanced at this conc.

(iii ) Presence of Fluorine in R.P. – The conc. varies from 10–14% or P2O5 in R.P. The HFacid in formed between reaction of R.P. and H2SO4.

(iv) HF has a great affinity for silica:

6HF + SiO2 = H2SiF6 + 2H2O

However, HF is more aggressive acid in corrosion process than H2SiF6 (Fluosilicic acid).

(v) Presence of Chloride in R.P. beyond .01 – .05 limits enhances pitting in metals.

Table 6Analysis of single super Phosphate

Single super phosphates contain mono, di and tri calcium super phosphates along with ironand Al sulphates, calcium fluoride and gypsum. Typical analysis of single super phosphate is asbelow:

P2O5 (W.S) = 18% (6% as free acid corresponding to 8.3% H3PO4)

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Water = 5.39 (Water of constitution)

P2O5 (Citrate soluble) = 0.40

P2O5 (insoluble) = 0.46

CaO = 26.6

F = 1.1

SO3 = 31.3

Fe2O3 = 0.48

SiO2 = 1.75

MgO = 0.14

Al2O3 = 0.25

Capital CostThe capital cost (1990) of a 600 MT/day phosphoric acid plant is of the order of US dollar

26.9 million + 50% cost for off sites facilities. The break up cost is as follows:

R.P. storage = 4.4%, Phosphate rock grinding = 17.6%, reactions and filtration = 44.9%, acidconc. = 14.7%, gypsum scrubber and ponds = 15.3% and acid storage = 3.3%. This is as perEuropean conditions.

TSP contains 46% P2O5 and is also called concentrated super phosphate.

New technology for phosphoric acid manufacture:

Israel Mining Industry has developed a process using HCl for manufacture of phosphoric acidinstead of H2SO4.

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30Chapter

ELECTROPLATING PROCESS

In plating process, metallic ions in the electrolytic bath are reduced and deposited on cathodeas a metallic coating when current of required density and voltage (D.C.) is passed to bath. Theanode can be the pure metal, being deposited in soln. or it can be insoluble anode, usually carbonrod, when metallic salt of the metal is reqd. to be added to the electrolyte to maintain concentrationof metal ions.

The electrochemical process is controlled by (1) Faraday’s laws of electrolysis (2) Standardsingle electrode potential and (3) Ohm’s law. Faraday’s laws gives the quantity of materials deposited,being directly proportional to the amount of current flow and its duration. It is inversely proportionalto the oxidation state of metal in the electrolyte. Ohm’s law gives the flow of current being directlyproportional to the applied D.C. voltage and inversely proportional to the resistance of the system.The internal resistance of the electrolyte bath depends on various factors.

Standard single electrode potential of the metal to be deposited, gives min D.C. voltage forplating. The actual voltage reqd. is determined as per various competing reactions in the bath. Singleelectrode potentials are given in table 18 (vol. IIA). A normal H2 electrode is used to determinepotentials of other metals.

As per Faradays Law W = CtZ

where W = wt. of ions deposited, C = Quantity of electricity passed, coulombs (current inamps × time in secs) t = time in secs, Z = Electro chemical equivalent of metal ion or wt. of iondeposited by 1 Amp current in 1 sec.

96500 coulombs of electricity (1 Faraday) is reqd. to deposit/liberate 1 gm. equivalent wt. ofany element.

As per Ohm’s Law – c =V

R

where c = current flow (amps) V = potential difference, (Volts) R = resistance, (Ohms)

Standard single electrode potential of a metal in soln. of its salt containing one gm-ion of themetal per litre and a normal hydrogen electrode. The e.m.f. of a electroplating bath is the differenceof single electrode potentials of electrodes in the bath.

1. TYPES OF ELECTROPLATINGThere are five types of plating processes of coating on base metals:

207

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1. Rack Plating

2. Barrel Plating

3. Spot plating or brush plating

4. Pulse plating

5. Non electrolytic deposition

1. Rack PlatingParts to be plated, are fastened to fixtures (cathode) in the plating bath where it is immersed

either manually or some auto processes. The fixtures carry the plating current to the parts.

2. Barrel PlatingThe parts (pins, clips, lip stick cans, buttons etc.) which are small pieces are put in a plastic

hexagonal perforated container which is rotated either manually or automatically through the electrolyticbath. The parts slowly tumble while the barrel is rotated and all are exposed to the plating action.Current is supplied through various types of controls into the mass of parts where it is transferredpiece to piece by contact during rotation.

3. Spot Plating or Brush PlatingHere plating is not done by total immersion only. Using anodes, surrounded by absorbent

material that do not require immersion of parts and portable equipment for spot plating is done. Theanode is a saturated soln. which is rubbed over the surface area to be plated. Very high localisedcurrent density is used because of movement and abrasive action on absorbent material. This is apatented process till 1995. This is suitable for electrodeposition of worn out machine parts.

4. Pulse PlatingThis is immersion plating with the difference that current is passed in short intervals of higher

intensity followed by stoppage of current. Each cycle is indicated as ratio of on time/off time dutycycle in % and the frequency of time length of each cycle. Not all metals can be used here fordeposition as some metals can not tolerate variation in current flow more than 5–10%. The processwas under research till 1996.

5. Non Electrolytic DepositThere are three types of deposit, namely immersion or displacement deposit, noncatalytic

chemically reduced deposit and catalytic chemically reduced deposits.

2.0 ELECTROPLATING BATH AIDS

Various chemicals are used for pH control, good plating quality, brightness, hardness of depositsetc.

(a) Rack Gold Plating on Copper or Copper AlloysGold plating solution:

Gold chloride = 2 gms/lit (0.27 oz/gallon US)

Pot. cyanide = 0.025 gms/lit

Pot. pyrophospate = 80 gms/lit

Bath temperature = 65–87°C

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ELECTROPLATING PROCESS 209

D.C. voltage = 6V

Current density = Amp/cm2

Anode = S.S.

Anode-cathode ratio of area = 3.1

N.B. Technical grades of chemicals should be used for better results.

(b) Tin Plating on IronTin plating solution:

SnCl2H2O = 15 gms/lit (2 oz/gallon US)

NaOH = 19 gms/lit

NaCN = 7.5 gms/lit

Hot boiling soln. is used

D.C. voltage = 6V

Current density = Amp/cm2

anode-cathode ratio of area = 2.1

(c) Cadmium PlatingCdO = 30 gm/lit.

sod. cyanide = 40 gm/lit or

Cd cyanide = 40 gm/lit

Anode-cathode ratio of area = 2.1

D.C. voltage = 4–6 V

Current density = Amp/cm2

Efficiency = 95%

Temp. = 20–35°C

Total NaCN/Cd = 3.75 : 1

D.C voltage = –

(d) Chromium PlatingCrO3 + H2SO4 + catalyst soln. = 250–350 gms/lit

CrO3/SO4 = 75 : 1 or 125 : 1

Temp. = 32–43°C (decorative articles)

37–65°C (hard deposit)

C.d. = 10–20 Amp/dm2 (decoratives)

= 15–35 Amp/dm2 (hard deposit)

(e) Copper PlatingCuCN = 22.5 gms/lit

Sod. cyanide = 34 gms/lit

Sod. chromate = 15 gms/lit

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NaOH = as reqd. to adjust pH

Analysis : Cu = 16 gm/lit

Free CN = 7.58 gms/lit

Temp. = 32–43°C

C.d. = 1–1.5 Amp/dm2

Voltage = 6 V

Anode Cathode area ratio = 1.1

Efficiency = 30%

(f) Bright Gold DepositKAu (CN)22H2O = 4–16 gm/lit.

KCN = 15–90 gm/lit.

Pot. carbonate = 0–30 gm/lit.

Pot. Phosphate = 0–45 gm/lit.

KOH = 10–30 gm/lit.

Brightner = 0.1–10 gm/lit.

Temp. = 15–25°C

C.d. = 0.1–0.5 Amp/dm2

Agitation = Reqd. (moderate)

Anode = Platinum/SS or gold

DC voltage = 6–12 V

Anode-cathode area ratio = 3.1

(g) Pure Aluminium MetalPure Aluminium is made by electrolysis (which forms the cathode where Aluminium is deposited.

The anode is the crude metal rod. The electrolyte is AlCl3. Voltage maintained is 4V D.C.

(h) Aluminium ProductionAluminium production by electrolysis of pure bauxite in a cell house containing a large no. of

cells called “pot” which are connected in parallel at 4V.D.C. Bauxite is mixed with cryolite (Sod. Alflouride) in reqd. proportion and 8% Calcium flouride is used to reduce melting temp. to 1000–950°C. Crude Aluminium is deposited on cathode which forms bottom of the pot and oxygen isliberated on carbon anode rods, suspended in the bath. Oxygen then reacts with carbon of anode

to form CO2/CO. For maximum current efficiency, wt. ratio of 3

NaF

AlF is maintained at optimal level

and AlF3 is added at regular interval to compensate the volatility loss. Bath is maintained 12–15°Cover the melting point. The polarities of cells (anode and cathode) are changed at intervals to overcome polarisation.

3. OTHER CONSIDERATION IN ELECTROPLATING(i) Strike soln.–The sol. is so designed as to deposit thin layer at relatively high c.d.

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ELECTROPLATING PROCESS 211

(ii ) High over voltage–maintained to overcome high hydrogen deposition potential at cathode.

(iii ) Covering power–higher c.d. to deposit metals in recess/bodies.

(iv) Throwing power–ability of soln. to deposit higher coating thickness of metal into lowcurrent density area.

(v) Depositing potential of metal–It should be lower than that of hydrogen.

(vi) Alloy plating–Two or more metals of alloy should be present in electrolyte and theirdeposition potential is sufficiently close.

(vii ) Stabiliser–It is an additive to electrolyte to prevent oxidation of iron or Fe+2.

(viii ) Brightener–Additive to ensure brightness of coating by modifying grain structure.

(ix) Cathode coating–When the protecting metal is situated below the protected metal in thee.m.f. series. Example–Tin plated iron. Whenever tin losses integrity, bared iron comesin contact with moisture and a galvanic couple arises where tin serves as cathode (+veelectrode) and iron as –ve electrode (anode). The electron flow from bare iron surfaceto tin where they discharge H ions while iron decays sending more and more iron intosoln.

(x) Anode coating–It is reverse of cathode coating.

3.1 Signs of Cathode and AnodeSigns of cathode and anode terminals are exactly opposite to those in galvanic cells where

anode is –ve electrode and cathode is +ve electrode while in electroplating or electrolysis, on thecontrary, cathode is –ve electrode where ions give out charge and anode is +ve electrode wheremetals go into soln. as +ve charged ions.

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212 REFERENCE BOOK ON CHEMICAL ENGINEERING

1. Cooling towers and spray ponds are devices for the cooling of water by transfer of heat, fromhot recirculated cooling water from factory plant facilities. The c.w. gains sensible heat fromvarious heat exchangers; by exposing the surface of hot water to incoming / surrounding airwhich cools the water by partly evaporating the hot water so as to remove the latent heat ofwater and also a part of sensible heat of hot water is removed. This is due to difference intemperature between hot water and incoming/ surrounding air to the cooling tower system orspray pond. The total heat thus removed to the air from the hot recirculated water in the coolingtower, or spray pond is the sum of latent heat of evaporation and sensible heat. The airtemperature must be lower than the hot water temperature. The cooling of water in coolingtower or spray pond takes place upto and below the wet bulb temp. of air in warmest summermonths.

Cooling Tower Types(i) Induced draft mechanical tower.

(ii ) Forced draft mechanical tower.

(iii ) Parabolic chimney type cooling tower.

(iv) Spray ponds for smaller cooling duty.

Out of two types of mechanical draft cooling towers only Induced draft tower with fan at thetop of tower is widely used because there is no chance of short circuit of moist hot humid air, asfound in forced draft tower, with fan at the bottom of tower. I.D. cooling towers can be groupedin a row of several towers depending on cooling duty and water rate, per unit cross section, is 2-3 times more than that of natural draft towers. In I.D. cooling tower maximum approach to W.B.temperature is economically possible. Running cost of mechanical draft C.T. is higher due to powercost of fans. Hot water is put into the sump at the top of tower and it flows into C.T. through nozzlesat the top deck. Splash bar fills inside the tower gives the increased area of contact of water withthe air.

Wind velocity below 4 km/hr is suitable for I.D. tower; cooling approach, upto 5 °F. of W.B. temperature of air is possible during summer months for design purpose. I.D. cooling towers havedouble entry of air through lowers at two sides and air and water flows counter currently.

In mechanical draft cooling towers, hot water from plant facilities is directly taken to the topand flows through two flapper valves into top deck having plastic nozzles for flow of hot water intothe basin. Cooling water level in top deck is kept at 3"–5" height.

31COOLING TOWERS

Chapter

212

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COOLING TOWERS 213

Natural Draft Cooling TowerThese are hyperbolic tall, usually concrete, towers with hot water spraying arrangement at the

top through which water falls through the empty tower without any splash bars. Air enters at thebottom of the tower and flows upward by the draft produced due to difference of temperaturebetween top water zone and bottom zone of cold water. Operation and maintenance cost is low butdrift loss from top is more and cooling approach is lower. Wind velocity, higher than 4 Km/hr issuitable but precipitation loss is more. First cost is higher.

In natural draft cooling tower hot water pump, at the bottom of the C.T., boosts the pressurefor sending hot water to the top sprayers due to higher head required to lift the hot water. Thisincreases the operation cost. Cold water pump usually recirculates the cold water to the plant.Thermometers are used for measuring Hot and Cold water temperature and pitot tube is used formeasurement of cold water flow. Hot and cold water header pressure measurement are usuallyprovided.

2. SPRAY PONDHere hot water is sprayed through a series of spray nozzles in cold water pond and temperature

of water comes down due to sensible heat transfer and evaporation which removes the latent heat.The heat duty is less and operational cost is the least. Cold water is recirculated to the plant facilitiesfrom spray pond.

In general for all types of cooling water systems emergency cooling water circulation pumpswith stand by emergency power, are usually required to run the pumps/critical equipment on powerfailure. A pit pump provision for draining of cold water basin is usually kept as well as cold wateroutlet strainers for cold water outlet to cold water pump, are provided.

3. DESIGN CRITERIACooling approach: It is the difference between cold water and wet bulb temperature of water.

A minimum of 5°F cooling approach during summer months is possible.

Dew point temperature: Temperature at which air-water mixture is saturated with water vapour.

Cooling range: It is the difference between hot water temperature and cold water temperature.

Wet bulb depression: It is the difference between dry bulb and wet bulb temperature.

The following parameters are required for designing a cooling system.

(i) Quantity of water to be cooled, m3/hr.

(ii ) Wet and dry bulb design temps. selection.

(iii ) Air velocity through the towers. m/sec.

(iv) Maximum and minimum dry bulb temperature.

(v) Hot water and cold water temps required.

(vi) Height of tower, m and tower fill volume, m3.

(vii ) psychrometric chart of air at atmospheric pressure.

4. PERFORMANCE COEFFICIENT OF A COOLING TOWERThis is based upon the heat dissipated per square metre of cross-sectional area of cooling tower

per degree C/ degree F cooling approach to the wet bulb temperature.

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214 REFERENCE BOOK ON CHEMICAL ENGINEERING

Performance co-eff =( )( )2 .

t tW

S t tw1 w2

a w w b

−− kcal/hr m2 °C

Where W = Cir. rate, m3/hr.

Sa = Packing area. m2

tw1 = Hot water temp. °C.

tw2 = Cold water temp. °C.

tw.b = Wet bulb temp. °C.

5. PSYCHROMETRIC CHART AT ATMOSPHERIC PRESSUREThe relation between dew point, saturation point of air and specific humidity of air is given by

Psychrometric chart. It shows saturation curves for air at different % saturation upto 100% saturation(dew point curve) at different dry bulb temperatures in horizontal axis vs partial pressure of watervapour in air as well as specific humidity in vertical axis. See psychrometric chart in chapter 44

Dew Point and Humidity(i) Dew point temperature can also be found out from steam table by knowing partial pressure.

Dew point remains constant so long air remains unsaturated. Dew point rises if some additionalmoisture is added to the air as partial pressure of water vapour rises.

(ii ) Wet bulb temperature is the dynamic equilibrium temperature attained by water surfaceexposed to air when the sensible heat transfer from air to the water surface is equal to the latentheat of evaporation of water carried away to the air from the water surface.

(iii ) Percentage relative humidity – It is the ratio between partial pressure of water vapour atany temperature to the difference between total pressure less partial pressure of water vapour at thesame temperature.

(iv) Dry bulb temperature – It is the ambient air temperature.

(v) Percentage humidity of air – It is a ratio between kg of moisture carried in 1 kg of dryair at the desired temperature to the amount of water vapour carried by 1 kg of dry air at saturation.

6. SIZING OF COOLING TOWERAs per graphical method given in Perry'.

7. COOLING TOWER FANThese are motor driven axial 4/8 bladed cast aluminium fans with reduction gear box located

at the top of cooling tower (I.D. tower). Air swept volume through the tower is one of the keyfactors in proper performance of cooling tower. A medium height chinmey around perimeter of fanssweep is installed for providing required draft of air.

In F.D. cooling tower fan is located at the base of cooling tower.

8. COOLING TOWER MATERIAL OF CONSTRUCTIONNormally Ascu treated wood (Pine, fur etc.) is used for construction of C.T. structure, splash

bars, desks, fan chimney, stairs etc. S.R.P. grid support is used for splash bars. Two end coversare made of asbestos sheet and also the louvers at opposite sides. Concrete cooling tower body isalso made.

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COOLING TOWERS 215

Cooling tower basin is made of R.C.C. work. Water level is kept at about 6–11 inches abovethe wooden support base in C.T. basin. Basin cold water outlet is provided with double S.S. screen.Make up water is added to the basin through float actuated control valve as per C.T. basin level.

9. WET BULB TEMPERATURE CALCULATION

Formula ′t = tk

hhw

fgfg− ′ −× 1 W Wb g

Where ′t = Wet bulb temperature °C.

t = Dry, bulb temperature °C.

Kw = Diffusion co-eff. of water vapour through film of air watervapour mix, kg/sec. m2.

h1fg = Enthalpy of vapourisation at wet bulb temp. kcal/kg.

hfg = Enthalpy of vapourisation at dry bulb temp. Kcal/kg.

′W = Spec. humidity at wet bulb temp, kg moistre/kg dry air

W = Spec. humidity at dry bulb temp, kg moistre/kg dry air

10. COOLING TOWER BLOWDOWNThe blowdown rate from a cooling tower depends on allowable concentration build up of a

constituent in make-up water. Usually a conc. cycle of 2–3 is maintained in circulating water.Formula for concentration ratio.

Concentration ratioConcentration of a constituent in cir. C.W.

Concentration of the constituent in m.u. water.=

This indicates concentration of one constituent in m.u. water and can go upto twice or thricein circulating water. The blowdown rate from cooling tower basin is to be kept accordingly. TheC.T. blowdown valve pit is kept at the back of the cooling tower. The C.T. blowdown water is neverto be discharged into the factory storm water drain. This is taken separately through pipeline to C.W.treatment plant as C.W. is always treated usually with chromate-phosphate dosing in the range of10 ppm chromate and 20 ppm phosphate for corrosion control of C.W. pipelines and connectedequipment.

11. M.U. COOLING WATERA continuous flow of make up water is needed to compensate for evaporation loss, drift loss

and blowdown loss of circulating water.

M.U.water flow = evaporation loss + drift loss + blowdown water. Usually evaporation lossis calculated @ 1% of circulating cooling water flow per 12° F cooling range (difference betweenHot return cooling water temperature and cold cooling water temperature both in same temperaturescale). Drift loss is taken as 0.1–0.2% of circulating water flow. Blowdown rate is as per concentrationcycle adopted.

12. PRESSURE DROP IN CIRCULATING COOLING WATER CIRCUITThe sum of the pressure drops in various cooling water loops (incoming and outgoing) in the

plant should be zero. This is as per Hagan-Poiseuille’ equaiton. The cooling water pump pressure

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216 REFERENCE BOOK ON CHEMICAL ENGINEERING

should be sufficient to send the cooling water to the remotest plant facility and allow the returncooling water to rise to the top of cooling tower. C.W. pipeline sizing is to be done consideringproper velocity of water.

13. TREATMENT OF COOLING WATERTreatment of cooling water is required to keep the rate of corrosion of carbon steel of C.W.

pipelines and connected equipment to min. level. Usual method is to put required quantities of sodiumdichromate and sodium hexametaphosphate so as to keep a concentration of chromate-phosphate inthe ratio of 10 : 20 ppm.

For control of pH of circulating cooling water, usually alkalies are put into cooling water soas to make the pH at 6.9–7.3. The pH of cooling water will, however, depend on the make up waterpH and presence of sulphate reducing bacteria in a circulating cooling water. Now a days insteadof phosphate-chromate treatment which requires reducing Hexabalent chromium to trivalent chromiumin the blowdown cooling water, the quaternary ammonium compounds are used to control corrosion,pH, and sulphate reducing, nitrifying and other bacteria, algae and fungi growth. Use of the quaternaryammonium compounds in required doses depends on test runs with the dosing chemicals. Thechemicals are, however, costly. Manufacturers claim that no treatment of C.T. blowdown is required.Microbiological analysis of c.w. is to be carried out.

14. RATING OF COOLING TOWER DUTYIt is usually expressed as quantity of cooling water circulation rate in m3/hr at design hot and

cold water temps based on basic data, supplied by customer or as amount of heat to be removedin KW or MW units (kcal/hr). One KW of heat removal is equal to 856.8 kcal/hr.

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32PAINTS AND PAINTING

Chapter

1. COLOUR SIGNIFICANCE(i) Attention galling: Various colours of paints cause attention in the following decreasing

order.Red – orange

Red – blue

Yellow

Pink

and luminous yellow– green.

(ii ) Adding coolness or warmth: Red–orange (hottest), reds and yellows. Blues and theviolets convey coolness.

(iii ) Creating moods: For stimulation and excitement, warm colour especially red–orange, redand orange. Blue–violet, violet and blue colours are subdued colours and tranquillizing colours areyellow–green, green and blue–green.

(iv) Suggesting size: For spaciousness, use. whites and lime blues.

(v) For feeling of closeness and confinement use dark colours.

(vi) Camouflaging: To hide overhead structures, extend wall colour to whole area. To hidepipes projections etc., paint them with the same colour as their surrounding.

(vii ) Saving on light: Use highly reflective colours (ceilings-white), Light reflection factors aregiven in table.

2. PAINTSPaints are homogeneous mixtures of paint vehicles and pigments. Paints are used mainly for

protective treatment of base materials, metals or wood mainly for decorative purpose.

2.1 Typical Components of Paints or Lacquers2.1.1 Paint vehicles:

(a) Non Volatile –(i) Oils (triglycerides of fatty acids)(ii ) resins

(iii ) Dryers(iv) additives

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218 REFERENCE BOOK ON CHEMICAL ENGINEERING

(b) Volatile—aromatics, chem and industrial solvents and lacquer solvents, ketones, esters andacetates.

2.1.2 Pigments.(A) Opaque

(B) Transparant

(C) Special purpose.

2.1.3 Oils. Alkali refined Kettle bodying linseed oils are mostly used. Soyabean oil, Tungoil, (china wood oil - Kettle bodying) Tall oil (combination of fatty acids andresins) are used in some types.

2.1.4 Synthetic resins – (a) Phenolic resins

(b) modified phenolic resins (ester gum and pure phenolics).

(c) maleic resins used in shorter oil lengths (made by reacting maleic acid or anhydritewith a poly-hydric alcohol such as - glycerine in presence of rosin or ester gum).

(d) Alkyd resins (made by reacting phthalic acid or anhydrite with glycerine andpentaerythritol which are further modified with drying or nondrying oils which aremostly used in synthetic enamel paints or industrial paints.

(e) Urea resins (Urea formaldehyde). It is usually combined with alkyd resins or plasticisers(suitable for metal painting).

(f) Melamine resins (made from malemine and formaldehyde and give better finish thanurea formaldehyde-expensive paint for colour retention.

(g) Vinyl resins (co-polymers PVC and PVA). available as white powder to be dissolvedin strong solvents such as esters or ketones - Paint has maximum resistance tochemicals, acids, alkalies, solvents and water. Used in cables, swimming pools, cars,masonry etc.

(h) epoxy resins (These are epichorohydrin bis-phenol resins, have chain structurecompound of aromatic groups, made from aromatic groups and glycerol. Variousmodifying agents are used to give epoxies of different properties.

(i) Polyester resins (made by Polymerisation of styrene and lower m.p. resins which areused in paint suitable for use including, varnishes and water proofing paper etc.).

(j) Polyester resins (polyester polymer with oils have good adhesive to metals - used inindustrial type paints.

(k) Silicone resins (Polymerised resins of organic polysiloxanes have excellent chem.resistance with high heat or electrical resistance–a very expensive paint.

(l) Rubber brand resins (Synthtic rubber paints have high resistance to water andcorrosion and used in swimming pool concrete floor, asbestos sheeting, exteriorstructures.

(m) Urethanes ( resins with alkyds type which are widely used as floor finishes andexterior clear finishes on wood.

2.1.5 Dryers. Facilitate drying of paints. Mostly dryers are metallic soaps that act as apolymerisation or oxidation agents or both. Soaps must be soluble in paint vehicle. Talloil dryers are less soluble than napthenate based on naphthenic acids. Other dryer normallyused are:

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PAINTS AND PAINTING 219

1. Cobalt drier – 6 – 12% cobalt metal in most powerful drier used in industry. It hasan oxidation catalyst. Excessive amount of cobalt drier can result in wrinkling. It ispurple in colour and shall not discolour paint.

2. Lead drier – 24 or 36% lead metal. This drier has been replaced by calcium orzircomium based drier.

3. Calcium drier – acts as a polymerisation agent and sold as 4,5 or 6% calcium. It ismore popular.

4. Zirconium – 6, 12, 18% Zirconium often used in combination with cobalt andcalcium drier.

2.1.6Additives. Used in a small quantity, its name and percentage are kept secret bymanufacturers. They belong to the following trade names.

(i) Antisetting agents (gives a gel structure with the vehicle).

(ii ) Antiskinning agent – Common name methyl ethyl ketone (used in alkyd paint).

(iii ) Bodying and puffing agent – used to increase viscosity.

(iv) Antifloating agent – used to supress separation of colours when two or more coloursare used.

(v) Loss of dry inhibitors – certain colours (black, organic red or TiO2) tend to activatethe drier and paint looses drying agent on ageing. Agents added, try to react slowlywith vehicle and additional drier added to replace what was lost. Now cobalt baseagents are used.

(vi) Levelling agents – special wetting agent is used to cause vehicle to net the pigmentwhich will not leave any brush or roller mark.

(vii ) Foaming prevention – Found in water based paint and debubbling agent is added.

Grinding of pigments – Additives are added during grinding of pigments which helpin melting.

Fungicides – added to prevent its development in exterior paints.

Antisagging agent – to prevent runs or sags of paints.

Glossing agent – to increase gloss.

2.1.7 Lacquers. Dry by evaporation of the solvent – they are either cellulosics, resinous andplasticizers (non volatile). A combination of cellulosics and resins based lacquers is used.

2.1.8Solvents. (i) Commonly used petroleum solvents as, for example, white spirit distilationrange, 149–204°C, also called thinner or terpentine; faster evaporation rate is suitable forall paints except for flat finishes where heavy mineral oils are used. Even faster evaporationmineral oil (distillation range 93–112°C) is used and often called as VM and p. naphthais also used as all purpose thinner, EPA (U.S.) limit is 250 gm of volatile solvent/litre ofpaint. Special purpose naphtha with aromatic content reduced is used as thinner forcleaning. (ii ) Paraffinic hydrocarbons – BP 40–60°C, 60–80°C and 80–120°C and specificgravity 0.645–0.676 and aromatic content 1–5% are also used. (iii ) Aromatic solventsfrom coal tar distillation are also used in industrial and chemical coatings. They are havinglow boiling point chemical. Solvent power increases with increase in aromatic content.

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220 REFERENCE BOOK ON CHEMICAL ENGINEERING

(a) Benzol C6H6 BP 79°C

(b) Toluol C6H3(CH3)- BP 110°C

(c) Xylol (Type-1) C6H4 (CH3) (BR 138 - 144. 5°C). These are three types of Xylenes– 23°C xylene, 5°C xylene and 10°C xylene (o.m. and para), and naphtha (BR 149–177°C) – it has slow evaporation rate.

(e) Trimethyl Benzene, high aromatic petroleum fraction having 80–93% aromatic (BR100–211°C), FP> 32 °C.

(iv) Alcohols – Acetone CH3COCH3 – fast evaporating.

Ethyl Acetate, CH3COO C2H3 – fast evaporating and low cut.

Butyl Acetate, CH3COOC4H9 – good medium boiling solvent for lacquers. It has goodblush resistance.

Isopropyl Alcohol – BP 82.4°C, FP 12°C, S.P. Gravity 0.7925.

Its property is similar to ethyl alcohol.

n-Propyl Alcohol – Azeotrope Compound, 71.7% alcohol and 28.3% water. It dissolvesresin, shellac and Castor oil.

Ethyl Alcohol – C2H5OH containing 5% methanol. – Good latest solvent for lacquers andalso used for dissolving shellac. Methanol added to prevent consumption.

n- Butyl Alcohol - Medium boiling – popular latest solvent for lacquers. BP 118°C, FP37°C and SP. Grv. 0.811.

2.1.9 Pigments It gives hiding or obliterating power of paints i.e., coat's property in covering the surface

being painted. It also gives decorative effect of paints.

Relative hiding power of white pigments.

Hiding Unit

Lead Carbonate – 15

Lead Sulphate – 15

ZnO2 – 20

Lithophone – 25

Antimony Oxide – 28

Anatase titanium di-oxide 100

(Crystalline form very less used).

Rutile titanium di-oxide 125 – 135

(Crystaline form mostly used having

density of 240–250 kg/m3).

2.1.10 Extender Pigments Low cost raw material (RMC) and they are nonhiding pigments such as Calcium Carbonate,

talc and clay; percentage used is more if hiding property is to be imparted. Talc is magnesium silicate.China clay (Aluminium silicate) – mostly used in water based paint. Other extender is diatomaciussilica used to reduce sheen or gloss.

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PAINTS AND PAINTING 221

2.1.10 Protective PaintsAnother use of pigments apart from decorative purpose is protection of metal or wood surface

(e.g. Cuprous Oxide and tributyl oxide to give ship’s bottom property to kill barnacles and antimonyoxide gives fire retardant property. Higher the pigment power higher is the gloss property. Otherproperties are to control viscosity and to give very specific property of flourescence, phosphorescenceand electrical conductance.

3. TYPES OF PIGMENTSApart from white pigments, extender pigments (whiting calcium carbonate (most important),

Talc (magnasium silicate commonly used to give low sheen), China clay (solvent base coating) andother extenders (silica. diatomacious), black pigments (Carbon black and Lamp black) etc. are made.The pigment colours are given in table 170 vol IIA.

Metallic Pigments – Aluminium powder; non leafing type used to give high metallic look andleafing type for silvery look Aluminium paint should not be in acid or alkaline atmosphere. Zinc oxideand red lead are used as primers.

3.1 Colour wheelThis wheel as given in Fig.1 gives complimentary colour at diametrically opposite to each other.

4. INDUSTRIAL PAINTSThere are three generic types of resinous paints.

(i) Alkyds (ii ) epoxies and (iii ) Vinyls.

4.1 Industrial UsageAlkyds – When a polyhydric alcohol reacts with a poly basic acid, an alkyd resin is formed.

In refinery, alkyd paints are used.

Epoxyes – It is made by reacting epichlorhydrin with poly phenolic compounds or mono/diamines or other compounds, when epoxy resin is formed. It is suitable for solvent atmosphere andcertain types of caustic atmosphere.

Vinyls – Suitable for highly alkaline and acid atmospheres as well as areas subjected to extrememoisture and condensate.

4.2 Paint ThicknessPaint thickness on applications : Minimum dry coating thickness required, is 2–3 coats of

thickness, 4–5 mils. The instrument is called elcometer.

4.3 Cleaning for Painting(i) Thorough cleaning of paint surfaces by sand blasting (costly), wire brushes, knives and

emery papers are suitable and solvents are used for oils and grease removal.

(ii ) Application of paints is by hand brushes or spray guns, whenever required, in industry.After 1st coat application, the coating is to be given time for drying so that 2nd coat could be applied,3rd coat is required in special equipment.

(iii ) A good thinner is to be topped up on paints occasionally to restore paint consistency forthe consumption of paints in containers.

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222 REFERENCE BOOK ON CHEMICAL ENGINEERING

(iv) Atmosphere for painting – In humid atmosphere which hampers evaporation of paintvehicle. Also no painting when the ambient temperature is low.

(v) After each coat of painting application, check for holidays, thin spots, Pinholes, missed areaand general appearance.

(vi) Without proper cleaning of surface, painting will be poor.

4.4 Major cost in painting is cleaning operation which is of the order of 50–60% of cost of paints.

Yello

w G

reen

Yello

w

G reen

Greenish B lue Green

B lue G reen

Fig. 1. Colour Wheel. Complementary Colours are at Diametrically Opposite to each other.

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33BIOGAS PLANT (DOMESTIC USE)

Chapter

Capacity range = 60–3000 cft/day methane gas

A. MAZOR EQUIPMENT1. Digestor

1. This is the main equipment where bio gas (methane) is produced from cow dung and waterslurry by methanococcus micro organism. It is constructed by brick and cement mortar as a squareor rectangular shaped box of size : 2.50 mH × 2.5 mL × 2.0 mW (suitable for a family of 6–7persons) with neat cement finish on floor.

The Ht

depth ofslurry ratio is kept at 5–6.

Digestor bottom level should be about 0.5m from grade level. The digestor top is to be coveredwith wooden top cover to prevant escape of methane. Gas outlet pipe (pvc) of 1" I.D. to methanegas holder, where, an inlet valve is to be provided at digestor side near top edge.

2. Drying Tank (1+1)A small tank of capacity 3m3 of brick and cement mortar at below digestor slurry ht. is to be

made so that spent slurry from digestor falls through a 3" PVC pipe. The tank should have a drainprovision of 2.5" pvc pipe with closure by wooden circular wedge. The spent slurry tank bottomis to be made by brick work without neat cementing.

3. Gas Holder1. Circular steel gas holder of size 2 m dia. and ht. 3 m, has a capacity of 9.5 m3 (7–10 days

consumption) for a family of 6–7 adults. The gas holder foundation (circular) is to be constructedby brick and cement mortar at 1 m above grade level and dia of foundation should be 6" more thanholder dia with 3 equal pockets for bolting of gas holder foundation bolts of 25 mm dia × 300 mmlong with 1:2:4 concrete with the support plate of gas holder. A 1" G.I. vent valve for purging attop of gas holder and a 1/2" G.I. valve at bottom of gas holder for gas outlet, is to kitchen to beprovided ; and earthing wire (GI – 6 mm dia.) is to be connected from gas holder bottom plate toa 3 feet deep earthing pit.

B. PROCESSA slurry of cow dung and water is to be made first by putting 30–35 kg/day cowdung into

digestor in 1–2 days and then made into a slurry at a ratio of 1 : 1 (cowdung–water) by adding water;

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some cut straw is to uniformly mixed with slurry for better composition of spent slurry in dryingtank. Also pH is adjusted by adding alkali to slurry to make pH 6.8–7.2 maintain slurry level at0.4–0.5 m in the digestor. If necessary, more cow dung is to be added. Cover the digestor with thewooden cover. The total hold up time in the digestor is 20–40 days. Aerobic fermentation first startswith air inside the digestor for 3–4 days, followed by anaerobic fermentation which continues for17–35 days when methane gas, along with CO2, is generated in the digestor and is led into gas holderthrough outlet pipe. Methanococcus micro organism breaks the cowdung cellulose, generating methane(CH4) gas with some CO2. The top cover edge is to sealed by mud to prevent gas leakage.

The air inside the gas holder is to be purged out initially as methane enters the gas holder withopen purge value in the gas holder top and keeping the gas outlet valve in the gas holder closed afterpurging. Purging is to be done for a considerable period of time to prevent explosion, (explosionrange 5–15%). The gas holder outlet line to kitchen is also to be purged for 5–6 mins. After gasholder is purged and top valve closed, methane pressure develops in the gas holder.

hydrolysis

6 10 5 2 6 12 635 Cby acid bacteriacowdung

C H O n H O n C H O acidification°+ → → →

Methanation

3 4 2by bacteria3n CH COOH 3nCH 3nCO .carboxylic acid

→ +

Thermal efficiency is 30–50%. The calorific value of bio methane gas (with CO2) is 500. BTUper SCF or 4450 kcal/m3. Some recycling of spent biomass can also be done.

After methane gas generation stops, close the gas inlet from digestor; open spent slurry todrying tank. One drying tank is to be used and other are kept stand by. The compost manureremoved from drying tank is used for agriculture. Finally the digestor top cover is opened and spentbiomass cleaned – a part of which can be recycled. About 2 months time is required for propercomposting of spent slurry. The methane gas generation rate is about 0.23 m3 per kg of cow dung.

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34SUGARS

Chapter

A. MANUFACTURE OF CANE SUGAR(i) Preliminary Crushing and Extraction of Juice

The sugar cane is weighed and subjected to crushing to extract juice. Crushing is done in twostages in juice extractors or roller mills. The roller mills contain 9 rolls in sets of 3. In the beginningsugar cane is first lebelled and then cut into small pieces followed by crushing in 1st rollers when50% of juice is extracted. This is followed by crushing in 2nd and 3rd sets of rollers. Thecomposition of raw cane juice.

Water Sucrose Reducing Other organic Inorganicsugars compounds compounds

77–88% 7–21 0.3–3 0.5–1

(ii ) Screening of Sugar JuicesThe raw juice, as it comes from the mills, is contaminated with suspended matter, mainly

bagasse fibres and mud. Separation is carried out by screening either in stationery drags screeningor in vibrating screens, made of brass. The drags screens is a perforated plate (260 – 400 perforationsper sq. inch) screen fitted with a movable rubber scrapper which recycles the bagasse particles tothe crushers through a conveyor. In vibrating screen the openings are smaller usually 0.1mm butoscillations are more than 600 per minimum. The amount of bagasse that can be separated byscreening varies from 1–10 gms/per litre.

(iii ) Removal of Suspended Matter from Screened JuiceThe screened juice still contains about 1 – 10% suspended impurities (non-sugars) which

consist of waxy matter (lipids), pentosans, protein matter (non sugars) and Inorganic oxides (CaO,MgO, Fe2O3, Al2O3, P2O5, SiO2) and insolubles. These are partly filtered out by heating the juiceto its B.P. followed by centrifugation in a high speed centrifuge. About 0.05–0.1 gm/lit. of suspendedmatter is removed by this method. Heating removes the dissolved air, coagulates the proteinicnonsugars and pentosans. Fe2O3 and Al2O3 are partly precipitated and SiO2 is precipited partly incombination with sesquioxides.

(iv ) Clarification of the Raw Sugar JuicesThe residual suspended impurities and ionic dispersoids in the raw juice are separated by

clarification with lime. The non-sugar dispersoids, present in the sugar juice, are listed below.

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226 REFERENCE BOOK ON CHEMICAL ENGINEERING

% non-Sugars

(a) Hemicelluloses, pentosans (gums) and pectin. 8.5

(b) Proteinic compounds.

(a) Albumin 7.0

(b) Albuminoges and Pectoges 2.0

(c) Asparagine and Glutomin 9.5

(d) Glycine and Aspartic acid 15.5

(c) Organic Acid (Except Amino)(a) Aconitic, Oxalic, Succinic, Glycolic and Malic 13.0

(d) Colouring matter(a) Chlorophyl, Saccharetin, tannin etc. 17.0

(e) Waxy material (cane wax) 17.0

(f) Inorganic Salt

Phosphates, Chlorides, Sulphates, Silicates, 7.0Nitrates of Na, K, Ca, Mg, Al and iron

(g) Silica 2.0

Item (a) to (f) are present as collodial dispersion. Item (g) is present as molecular and ionicdispersion. Out of the above dispersoids some are removed in the heating and centrifugation operationsmentioned in step (III) above and remaining dispersoids are separated by liming process.

There are several clarification processes available, as stated below.

Lime Clarification ProcessLime clarification process is the oldest process using lime as the clarifying agent. There are

several modification of the process.

(1) Cold liming process

(2) Hot liming process

(3) Fractional liming process

(4) Fractional liming and double heating process

The other two clarification processes viz (5) Carbonation process and (6) Sulphitation process,are basically similar to lime clarification process since in the above two processes lime is also usedas the clarifying agent.

(i) Cold Liming ProcessLime is made into a slurry with condensate in a rotary slaking machine, or other types of

machine. The rotary slakes consist of slowly revolving, nearly horizontal cylindrical vessel, fittedwith baffles. Lime and water are fed at one end while the milk of lime is discharged from the otherend which is transferred to a settling tank where undissolved impurities collect at the bottom. Theslurry of lime over flows into a sieve (13 mesh) which is constantly sprayed with water.

The filtered milk of lime is stored in a tank, diluted to proper concentration and pumped to feedtank in the clarification section. The concentration produced depends on the process used – inSulphitation process it is 10–15° Be' or less and in carbonation process it is 20° Be'.

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SUGARS 227

Measured quantity of milk of lime is added to the cold raw sugar solution in the mixing tankprovided with agitator with manual, automatic or electric metered feeding device.

Some Phosphates are also added. The process is either batch or continuous as in a modernprocess. Lime addition is adjusted so that pH is maintained at 7.2–8.6 with constant stirring. Lime,Ca(OH)2 reacts with the non-sugars in the raw juice so as to (i) precipitate some of them as insolubleCa compounds or complexes (ii ) Coagulation of the colloidal and coarse dispersoids and (iii ) formsoluble Ca compounds and complexes.

The magma is heated in a heater and transferred to classifiers to flocculate and settle theinsoluble reaction product. The quality of phosphate in the raw juice measures the amount ofprecipitate to be formed in clarification process since more the phosphate contact, more will be theamount of precipitate. pH is an important factor in the liming process and the volume of precipitatedmass increased with increasing pH.

The insoluble solids settle to the bottom of the clarifier and are removed as dark colouredmatter (due to tannins). Clear sugar juice from the clarifier is then transferred to carbonation tank.

Feed to clarifier is either at centre of periphery and the flow is also either counter current orparallel current.

The clarifier used, are of multiple shallow tray types, having capacities ranging from 50–120cft per short ton of cane per hour.

(ii ) In hot liming process the raw juice is first heated to 100–102°C and milk of lime is thenadded to maintain a pH of 6–8.0 and the juice is allowed to settle.

(iii ) In the fractional liming process, pH level is raised to 7.6–7.8 in two stages-first liming at6.0 – 6.4 pH and then heated to 100 – 102°c and second liming at 7.6–7.8 pH, followed by settling.

(iv) Fractional liming and double heating process, which is similar to fractional liming processwith the exception that the magma is given a post heating operation after second liming, followedby settling. The first heating is also done at 93°C.

(v) Carbonation process: The excess lime present in the clarifier as dark coloured sugar juice,is removed by carbonation since it imparts syrups and molasses a very dark colour and also increasestheir viscosities, resulting in difficult crystallization operation, and also, the sugar that is produced,is of brown in colour.

The carbonation process is carried out either in a single stage or in two stages and consistsof bubbling CO2 through magma. The residual non-sugars are precipitated or adsorbed on the CaCO3crystals.

In single carbonation process, the sugar juice is mixed with 70 liter of 20° Be' lime per 1000liter of juice in the carbonator so as to make this sugar juice extremely alkaline. CO2 gas, from limekiln, is then bubbled through the mass till the solution shows a neutral reaction of Phenolphthalein.Carbonation time is 40–60 minutes. The juice is then filtered in filter presses.

In double carbonation process, the juice is heated to 55°C and 100 liter of 20°Be' lime is addedto 1000 liter of juice and the CO2 is then bubbled to the juice till the alkalinity of 400–600 mg CaOis attained. Most of the non-sugars are precipited in this stage, and filtered in filter presses.The filtrate is again carbonated till a slight alkaline reaction is observed on Phenolphthalein. ResidualCaO along with some non-sugars are precipitated as Calcium Carbonate in the second carbonationprocess. In second carbonation there is no foaming of the juice. The raw juice is again filtered infilter presses.

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228 REFERENCE BOOK ON CHEMICAL ENGINEERING

(vi ) Sulphitation ProcessThe process consists of adding excess lime as the clarification agent, followed by precipitation

of excess lime by SO2, SO2 is dissolved to form Sulphurous acid which reacts with Ca(OH)2 to giveCa2(SO3)2 precipitate.

There are two modifications in the process viz (i) single Sulphitation and (ii ) Double Sulphitation.The process is either batch or continuous. In (i) mixed sugar juice is heated to 75°C and taken ina preliming tank and milk of lime at a concentration of 6–15° Be' is added so as to make the pH7.4. The mixture is transferred to Sulphitation tank where SO2 is bubbled from the bottom of thetank which also gives the desired mixing effect. Some provision is made in the tank for circulationof the mass for good absorption and mixing.

The total filtering area required in single sulphitation process is 35 square metre per 100 tonof cane per day.

SO2 gas is produced by burning Sulphur in Sulphur burners using excess compressed air.

From prelimer, the juice is pumped to the sulphitation tank by a recirculation pump whosefunction is to circulate the juice in the sulphitation tank and to reduce the pH level in the prelimingtank by returning a portion of the limed juice to the preliming tank. pH control in sulphitation tankis done either by lime control or by SO2 flow adjustment. It is then filtered by sedimentation – themuddy juice is filtered in filter presses.

The double sulphitation process is a new development and consists of second liming to pH 10.5after first sulphitation. The juice is then heated to 65°C and filtered. The filtrate is again Sulphitedto neutral reaction followed by second filtration. The total filtration area required in this process is65 square metre per 100 ton of cane per 24 hour.

Comparison of the different clarification processes:

(A) No-sugars are removed more completely in carbonation process than in sulphitation processand lime clarification processes. (B) Sugar crystals obtained from carbonation process is more whitethan in other processes (C) Out put of sugar is more in carbonation process (D) sulphitation processrequires improvement.

(vii ) Evaporation for CrystalizationThe classified sugar juices from the sedimentation tanks, as well as from the filter presses, are

screened in a bronze wire mesh having 2000 meshes per cm square. The juice, having a pH of about7.1, is now concentrated in triple effect vacuum evaporaters with natural circulation and fitted withdown comer at a temperature of 103°C. The concentrated juice or syrup crystallises in U typecrystallizers (Swenson Walker Crystalliser) using fine sugar as seeds. Heat of crystallisation isremoved by circulating cooling water to the crystalliser. The magma is then centrifuged and washedto separate the sugar crystals. The separated mother liquor or molasses sent to vacuum pan feedtank. The primary molasses is then mixed with syrup and crystallised, followed by centrifugation.The separated mother liquor or molasses is sent to the storage tank via weighing scale forstorage and sold as a by product. Sugar crystals are dried in a rotary drier, cooled and directlybagged.

B. MANUFACTURE OF BEET SUGARThe important steps in the manufacture of beet sugar are.

(1) Extraction of juice from beet roots by diffusion

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SUGARS 229

(2) Clarification in two stages: First by double carbonation followed by Single Sulphitation

(3) Evaporation of clarified juice in five effect evaporators.

(4) Post clarification of syrup by single sulphitation

(5) Crystallization of beet sugar from syrup

(6) Separation of beet sugar from the slurry (beet molasses)

1. The Extration of Sugar Juice from Beet Roots by DiffusionThe beet roots containing sucrose in the cells, are washed and sliced into V shaped pieces,

called cossetes. The freshly cut pieces are put in the last cells of diffusion battery. The batteryconsists of 8–16 diffusions cells and work on counter current principle. Hot water is added on thefirst vessel and almost exhausted cosset are put into it. The residual sugar in cossetes diffuse intothe hot water and the weak sugar solution thus produced is sent to the second vessel after it is heatedup in a heater. The stronger solution from the second cell is then passed into the remaining vesselsin turns and in the last vessel, the rich solution is contacted with the fresh beet slices. The juiceleaving the last cell is having almost the same concentration as that in the beet itself and is sent forclarification. The juice obtained is purer than that obtained from cane sugar since gums and albuminetc., do not pass through the cell wall.

Diffusion process for cane sugar extraction is not possible due to deterrioration on longstanding.

2. Refining of Raw Beet Sugar

The raw beet sugar obtained is not perfectly white due to presence of impurities which areremoved by further clarification and recrystallization. The refining process of beet sugar consists of.

(a) Affination

(b) Re-melting

(c) Clarification treatments (i) liming (ii ) Adsorption on bone charcoal.

(d) Re-crystallization

(e) Centrifugation

(f) Drying.

Uses. By product molasses is mainly used for fermentation for alcohol – It is also used inrefractory to increase green strength, and as paste for charge chrome.

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35PHENOLS FOR DISINFECTION

Chapter

Phenols are antiseptics and disinfectants containing phenols (cresylic acid) and cresols.

Black Phenyls are cheap products whose specification is given in BS 2462–1961 (modifiedblack phenyl and modified white phenyl)

Black Phenyl: Homogeneous solutions of coal tar acids or similar acids derived from petroliumor any mix. of these with or without hydrocarbons and with a suitable emulsifining agent. Blackfluids are miscible, yielding stable emulsions with artificial hard water in all proportions from 1–5%.

White Phenyl: Finely dispersed emulsions of coal tar acids or any mix. of these, with orwithout hydrocarbons.

UK Brand names of white Phenyl: Sal-Hycol, Printol, Pacolin and R Crolin.

Modified black and white fluids may contain, in addition to above, any other ingredients, butif these are made the type and amount must be disclosed.

Classification as per germicidal value and method of testing employed. There are 6 designationsof black fluids.

(i) BA (Rideal–walker, R–W coefficient not less than 4)

(ii ) BB (R–W coefficient not less than 10)

(iii ) BC (R–W coefficient not less than 18)

(iv) BE (Chicks Martin, C–M coefficient not less than 1)

(v) BF (C–M coefficient not less than 3)

(vi) BG (C–M coefficient not less than 4.4)

There are 7 designations of white fluids, 6 of these groups WA, WB, WC, WD, WE, WF andWG has the same minimum R–W or C–M coefficient as the corresponding black fluids and the 7thwhite fluid group WD has a minimum crown Agent coefficient of 10 and minimum R–W co-eff.of 18. For modified Black and White fluids, the Phenol co-eff. (Staphylococcus) determined by aspecified method, must be stated by the manufacturer in addition to R–W co-eff.

Procedure Test norms

1. R–W test – BS – 541 Broth culture of specific micro organism.

2. Chick Martin test, BS 808 Yeast culture

3. Crown Agent's test, BS 2462 For white variety only, requires sterile artificial sea

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water dilution of disinfectant in presence of solubleand insoluble organic matter.

4. Phenol co-efficient test, BS 2462 This test is for ensuring that modified black andmodified white phenols are not unduly selective intheir bactericidal activity.

5. Manufacture – There are two important processes –

(1) Cumene oxidation (Hock's Process) and

(2) Toluene oxidation process.

6. Toxicity – It produces skin irritation and causes nervous systembreakdown. LD

50 human = 140 mg/kg body weight.

TLV limit is 5 ppm (CIS = 1.5 ppm)

7. Waste water treatment – 1–3% phenol is removed from waste water byfor phenol recovery cumene and acetophane extraction.

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232 REFERENCE BOOK ON CHEMICAL ENGINEERING

The Ferro alloys have higher percentage of iron. Usual ferro alloys are Ferro-silicon, ferro-manganese, ferro-chromium, Ferro-titanium, ferro-nickel, ferro-boron, and ferro-molybdenum etc.

These alloys are prepared by direct reduction of respective oxides or technical grade oxides orconcentrates with carbon (carbothermic process) or with Aluminium (alumino thermic process).Ferro-manganese, ferro chromium and ferro silicon are prepared by carbothermic reduction ofparticular oxides in submerged arc electric furnaces. Other raw materials, apart from correspondingoxides, is metallurgical coke and power requirement for the electric furnace varies from 15–100 MVA.

Ferro-manganese can also be produced in Blast furnace. Ferro-chrome and ferro-manganesehave high affinity for carbon and these alloys contain 7–8% carbon, while Ferro-silicon of 25% Si,contains 1% C and that containing 75% Si has 0.1% C.

Low carbon ferro-manganese (0.1–2% C) or ferro-chromium (0.02–2% C) is produced firstas a silicon containing ferro alloy using quartzite and coke in a submerged arc electric furnace. Thesesilicon containing alloys are then used for silicon thermic reduction process using an appropriateoxide ore in an arc refining furnace to get low carbon ferro-manganese or ferro-chromium.

Silico thermic direct reduction process with addition of Aluminium is used to manufactureferro-molybdenum and ferro-nickel. The energy released in the reaction is adequate to melt bothmetal and slag. Solidified block of ferro molybdenum or ferro-nickel can be recovered easily.

Ferro-vanadium is produced by using vanadium oxide, iron turning, stampings or rail bits andAluminium in a refractory lined open hearth furnace where heat of reaction melts both metal and slag.Often inert materials are added to lower the peak temperature. Ferro boron and ferro titanium isproduced in a manner similar to Ferro-titanium which contains 70% Titanium and 30% iron; usingscrap Titanium and iron apart from Aluminium and so also Ferro-Zirconium. Ferro-selenium isproduced by exothermic reaction of iron and selenium powder.

Steel industry uses these ferro-alloys to produce particular steel or alloy, containing the alloyingmetal with iron in ferro-alloys.

36FERROUS ALLOYS

Chapter

232

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FERROUS ALLOYS 233

Table 1Composition of ferro-alloys

Item Alloying metal Iron Carbon

Ferro-manganese Manganese – 75–92% 25–8%

Ferro-Chromium Chromium – 45–95% 55–5%

Ferro-Titanium Titanium – 20–75% 80–25%

Ferro-Nickel Nickel – 20–60% 80–40%

Ferro-Silicon Silicon – 8–9.5% 92–91%

Ferro-Silicon Silicon – 25% 75% 1%

Ferro-Molybdenum Molybdenum – 62–70% 38–30%

Ferro-Selenium Selenium – 50% 50%

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234 REFERENCE BOOK ON CHEMICAL ENGINEERING

37HIGH CARBON CHARGE

CHROME

Chapter

1. Charge chrome containing carbon and 50–60% chromium, is required for alloys like stainlesssteels. Typical analysis of charge chrome :

Cr = 50–56% or 56–60% wt%

C = 6–8% (max)

Si = 4% (max)

P = 0.03 (max)

S = 0.035 (max)

Size of product : 10–150 mm lumps; standard = IS 11945 (1987)

High carbon charge chrome is required for introduction of chromium in S.S. and special alloys;raw materials and utilities required are :

Chromite Ore = 2200–2500 kg/Te

Briquette Coke = 330 kg/Te

Lime = 156 kg/Te

Quartzite = 142 kg/Te

Molasses = 600 kg/Te (binder)

(Sugar = 85.5%)

Paste for electrode = 60 kg/Te (molasses)

and power (a) 3000–3100 kwh/Te (for Pelletising and preheating route)

(b) 3800–4100 kwh/Te

2. There are two routes for manufacture – by pellestising and preheating or by Briquette chargewithout preheating.

Charge Pelletising ProcessChromite Ore materials as per calculation is ground in ball mills to 80% below 200 mesh and

then formed into 15–20 mm balls in dicc pelletiser, for agglomeration, is used after adding coke andflux (bentonite 1%) in the charge. The balls are then preheated in a rotary static vertical klin with

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HIGH CARBON CHARGE CHROME 235

off gases from smelting furnace (to save energy in electric smelting furnace as much as 0.7–0.8kwh/Te). Preheating of pellets makes it hard. The preheated pellets are then melted at 1600°C in anelectric submerged arc furnace of capacity 30–45 MVA and voltage 150–160 V with circularstationery hearth with self baking continuous soldering electrode holder assembly as well as electrodestripping mechanism, copper contact clamps for holding electrodes, water cooled copper bus barswith copper tubing. Coke reduces the chromite ore at high temperature.

3Cr2O3 + 18/7 C = 4/25 Cr7C3 + 2CO

FeO + C = Fe + CO

1/3 Cr7C3 + 1/3 Cr2O3 = Cr + 3CO

The cast housing provides metals and slag draw outs with guns for closing of tap holes andrefractory lined laddles for holding tapped molten metal and slag.

Slag granulation plant, crushers are available in the facility along with raw material handling andwarehouses. Slag volume is 1.2 to 1.4 times to that of metal. The chromium metal on cooling iscrushed into 10–150 mm lumps for use in alloy steel furnace for chromium addition.

Off gase from submerged arc furnace, after it is used to preheat the pellets, is scrubbed in aventuri scrubber with alkaline water.

3. FLEXIBILITYHigh carbon charge chrome plants are usually designed for flexibility to produce ferro manganese

or ferro silicon.

Power savingBy plasma technology in electric smelter furnace of capacity 30 MW or more. Other power

saving processes by Kwasaki, In-metco and Krupp codir.

Lower capacity 2.5–5 MVA plants are also in use.

4. BREQUETTING OF RAW MATERIALSThe grounded ores, after benificiation, are mixed with binders (molasses and lime) and fed to

a double roll briquetting press to form 50 × 40 × 25 mm shaped bricks.

In the west, molasses binding material is not used for obvious reasons. Beneficiated ores givebetter quality charge chrome.

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CHARACTERISTICS OF VALVESUSED IN CHEMICAL PROCESS

INDUSTRY

Chapter

38

1. CRITERIA FOR USE(i) Material of construction; for body and trim (Stem, seat ring, disk)

(ii ) Valve standard – codes and type-rising stem or non rising stem.(iii ) Connecting flanges – Flat, raised face and grooved flange.(iv) Valve functions, on-off, throttling, pressure regulation or relief, preventing back flow or

combination.(v) Press. drop consideration.

2. (a) Gate valve, if used, in throttling service, produce wire drawing.

(b) Globe valve throttling efficiency is more due to increased resistance to flow for size upto 6".

(c) Plug cock valves are more +ve shut-off than gate valve and can be used for throttlingbut characteristics are not as satisfactory as glove valve for such service, with lowerpressure drop. Non-lubricated plug valves work by cam-crank mechanism. Excellentservice, for corrosive service which requires special lining or alloys.

(d) Swing check valves have minimum pressure drops and suitable for liquids and for largerline size. It is not suitable for pulsating flows. Some types work only in horizontal lines.

(e) Piston check or drop check valves are suitable for vapours, steam, water and pulsatingflows.

(f) Y-type valves produces lower pressure drop and turbulance than globe valve and ispreferred for erosive services.

3. Usually globe valve for flow control is used for sizes upto 2 ½" to 3" and beyond thesesizes, gate valves are used.

4. ASTM A 351 material valves of Ferrite and Austenitic steel castings are used for hightemperature service. ASTM A 182 material forged or rolled alloy steel, are used for pipeflanges, fittings for high temperature service.

5. Valves in oxygen service use molybdenum disulphide based lubricant to prevent firehazards.

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39BOILER FEED PUMPS AND

STANDARD VALUES FOR BOILERFEED AND CIRCULATING WATER

Chapter

237

BOILER FEED PUMPSDimensioning in accordance with the "Technical Regulations for Steam Boilers" governing the

equipment and installation of steam generators, edition of September 1964. German regulation.

Every boiler plant must be fitted with at least two feed pumps driven from two mutuallyindependent power-sources. In the case of steamdriven feed pumps, however, all pumps may beconnected to the same steam supply system. Electric feed pumps may be driven from the samepower source provided that, in the event of power failure, firing is also disconnected.

Where only two feed pumps are used, each pump must be capable of providing: 1.6 times thetotal steam output of all boilers to which it is connected, in the case of boilers not fitted withautomatic feed control up to 32 t/h.

1.25 times of this amount in the case of boilers of above 32 t/h or where there is automaticfeed control;

1.0 times the amount stated above in the case of once-through boilers.

Where more than two feed pumps are used, the pumps remaining in operation after the pumphaving the highest output has failed must be capable of providing at least the quantity of feed-waterspecified above for one of two pumps.

Feed Pressure

The feed pressure of the pumps must be sufficient, not only in delivering the quantities of feedwater required to overcome the maximum safe operating pressure, but also in delivering the feedwater quantity corresponding to the steam output, 1.1 times the maximum safe operating pressure,the resistances between feed pump and steam generator to be considered in each case.

In the case of once-through boilers, allowance must also be made for the pressure loss in thesteam generator at maximum steam output.

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238 REFERENCE BOOK ON CHEMICAL ENGINEERING

Power required at pump shaft N = 2.72 D.P

.ρ η in kW

where D = feed water quantity, kg/h

P = feed water pressure, atm. gauge

ρ = density of feed water, kg/m3

η = pump efficiency, %, namely:

60–80% for direct coupled centrifugal pumps and

80–90% for reciprocating pumps.

Select a motor rating approximately 15% greater than N.

Table 1

2. Standard Values Feed water

Constituent Unit Fire-tube Water-tube drum type Once-through-typeboilers boilers1 atm. g boilers and spray-

water for super-< 20 atm.g Heated-steam

202) 402) 642) ≥ 80 coolers

General – clear and colour lessRequirements

Hardnessmval

1< 0.04 < 0.02 < 0.01 < 0.01 Not detectable

Total carbondioxide mg/1 – < 20 < 20 < 20 < 1 <.1

Oxygen mg/1 < 0.5 max. 0.03: for continuous < 0.02operation

Iron mg/1 if possible < 0.05 < 0.03 < 0.02

Copper mg/1 < 0.01 < 0.005 < 0.005

Silicic acid Sio2 mg/1 Continuous operation without < 0.02blow–down, max. 0.02; otherwiseonly as required for boiler water

Potassium perman- mg/1 If possible < 10 if possible < 5 if possibleganate (KMnO4) < 5consumption

Oil mg/1 < 5 If possible < 1 < 0.5 < 0.3

ph.value at 20 °C – For all pressures 7.... 9.5 7..... 9.5

Continuous operation without blow–down

ConductivityS

cm

µ< 0.3 <0.2

at 20 °C otherwise only as required for boiler water

(1) Source : VGB Reports 1962. No. 76. pp. 1–3.

(2) With local heat transfers > 2.105 kcal/m2h, the standard values for pressures 80 atm.g shouldbe used.

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BOILER FEED PUMPS AND STANDARD VALUSES FOR BOILDER FEED.... 239

Table 2

3. Standard Values for Boiler Water

Constituent Unit Fire-tube Water-tube boilers1 atm.g boilers< 20 atm.g 202| 402| 642| 802| 1252| 160

P value mval/1 5.25 < 10 < 6 < 3 < 1 < 0.3" < 0.1

= 50mg < 15 < 5CaCo3/lit.

No restr- 3 3iction if

Silicic acid mg/1 P value and < 70 + 7p3) < 30 + 3p3) <10 < 4 < 1.2 < 0.4SiO2 P2O5 as

specified

Phosphate P2O54) mg/1 < 25 < 25 < 10 < 3

Conductivity at µs/cm < 8000 < 8000 < 5000 < 2500 < 1500 < 250 < 5020 °C

(1) See page 238.

(2) With local heat transfers......>2.105 kcal/m2h it is recommended that the standard values for 160atm. g (apert from SiO2 and p value) be used in all pressure ranges.

(3) p = p value

(4) May even be entirely omitted where the sudden appearance of hardness is reliably prevented.

(5) 1000 µs/cm is equivalent is approx. 500 mg NaC1/1 ∆ approximately 0.05° Be'.

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240 REFERENCE BOOK ON CHEMICAL ENGINEERING

CRYSTALLIZER CLASSIFICATION

Chapter

40

Table A

Mode of operation .... continuous Batchwise

Method of crystal suspention ..... Hydraulic, Mechanical Buoyancy, Fixed support

Method of crystal size control ..... Nucleation rate, Intermediate seed rate

Method of growth inducement ..... Evaporation, Cooling, Salting out effect

Table BEquipment Type and Temperature – Solubility Relationships

Effect of temp. rise on Equipment reqd. Example

solubility in water

Small increase in solubility Evaporator-crystallizer Sodium chlorideSalting out evaporator

Decrease in solubility Modified evaporator-crystallizer Anhy. sodium sulphate,Gypsum, Iron sulphatemono hydrate

Substantial increase in Vacuum crystallizer Water Potash alum, Glauber salt,solubility or brine cooling crystallizer Coppers, Potassium nitrate

Moderate increase in Modified vacuum or Evaporator- Pot. carbonate, Sodiumsolubility crystallizer nitrite, Pot. chloride

Source: Chemical Engineering, Dec. 6 1965

Solubility curves of various inorganic salts are given in Fig. 1 and Fig.2.

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CRYSTALLIZER CLASSIFICATION 241

Fig. 1. Solubility curve of various salts.

Fig. 2. Solubility curve of Sodium Sulphate.

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BRIEF ON OFFSHORE OILEXPLORATION AND

TRANSPORTATION PIPELINE

Chapter

41

THE SYSTEMThe two 6.625" O.D. oil/NG lines are fixed inside by spacers (segmented) in a 18" special steel

casing pipe. Both the gas/oil pipes as per ASTM standards are provided. with SECT heat tracingstubes, methanol control tubes (1.315" O.D.) and hydraulic control tubes (1.315" O.D.). The gas andoil pipes are provided with 25 mm thick polyurethene foam insulation. The inner pipes are providedwith rollers arrangement for free movement due to various factors – winds and waves, tidal currents,breaking waves, seabed topography, hydrostatic head. and sea bed soil resist, horizontal and verticalmovements due to environmental forces during installation and operation. The assembled casing pipeis laid on sea bed by pull from shore or pipe pull from lay barge, close to shore (common); crosssection of pipe is given in Fig. 1.

Spacer

M ethano l contro ltubes (1 .315” o .d .)

18 dia oute r casingstee l pipe in sea bed

′′

6.625” s tee l oil line insea bed

Pipe Ro lle rs

25 m m P o lyure thane foaminsu la tion

Hydrau lic contro ltube (1 .315” o .d .)

6 .625” s tee l gaslinein sea bed

M ethano l contro ltubes (1 .315” o .d .)

Heat trac ing tubes

Fig. 1. Offshore Oil/Gas Exploration Pipe line.

242

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GENERAL1. Insecticides or Pesticides are insect destroying substances of chemical, organic extracts from

medicinal plants. The insecticide action is through stomach poison, contact poison, systemicand non systemic poison, or act as repellants and attractants. Insecticides are broadly classifiedinto the following groups based on action on the type of pests.1. Acaricides (Mites destroying)2. Insecticides (Kill insects)3. Molluscicides (Action on snails)4. Nematocides (Action on underground eel worms)5. Rodenticides (Action on rats or mices and sqirrels)6. Slimicides (Remove slimes)7. Fumigants (Prevent deterioration of fruits and cereals)8. Fungicides (Kill fungus growth)9. Herbicides (Destroy unwanted vegetation growth)

Insecticides/pesticides can be solid or liquid and natural or synthetic. As per Indian insecticidesAct 1986 (Rules 1971) and (ammended in 1995) there were 143 pesticides for registration. PesticideBoard takes about 6 yrs for registration of a new Pesticide molecule. Indian insecticides 1968 Act,goes on changing due to new items or some listed ones deleted due to harmful effects. India is thelargest producer of pesticides.

Pesticide formulations are usually made by small scale producing units. Some of the newpesticides, listed in different groups below, have not yet been registered due to old patent Act andexclusively available in the west.

1.1 There are Six Types of Insecticide GradesE C = Emulsifiable concentrate.W P = Finely milled powders that form a suspension with water.

W S C = Water soluble concentrateA S = Alcohol soluble pesticide

W D P = Water dispersible powder.G R = Granulated formulation.

INSECTICIDE OR PESTICIDE

Chapter

42

243

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244 REFERENCE BOOK ON CHEMICAL ENGINEERING

Powder insecticides are ground with talc or clay with addition of wetting and dispersing agent.Antifungal pesticides are applied either on soil or as folier spray.

2. THE LIST OF VARIOUS PESTICIDES ARE AS FOLLOWS2.1 Group A – Acaricides

Name Area and action

1. Nimidane –

2. Amitraz – Fruit and hops

3. Apollo 50C – Top fruit

4. Azocyclolim – Fruit and Vegetable

5. Childien – Contact poison

6. Chexalin – Mites in fruit

7. Damfin – Stored grain

8. Dicofol – Mites killer

9. Dieno-chlor – Ornamental trees

10. Dimethoate – Insecticide and acaricide

11. Devipan – Agri. insecticide

12. Fen properthrin – Fruits and Vegetables

13. Malathion – Non systemic, contact poision and respiratory system attack.

14. Mesurd – Foliar feeding caterpillars and sucking pests.

15. Aqualin/cu. sulphate – Water body application

16. Methamidophos – Sucking and chewing insects.

17. Methomyl – Wide range and spider mite control.

18. Parathion – Systemic insecticide with contact and stomach action. Highlypoisions; suitable for wide range of insects.

19. Quinomethriorate – Fungicidal action

20. Fenovalerate – Termite killer

21. Dichlorophene

22. Fenithrion –

23. Suxon –

24. Para-quate –

25. d-allethrin (4%) – Mosquito repellant.

26. Hexachlorophenol –

27. Sisystox – Seed treatment and foliar spray, systemic.

2.2 Group B–Insecticides1. Arsenic trioxide

2. Alachlor

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INSECTICIDE OR PESTICIDE 245

3. CaO

4. Carbaryl – Contact insecticide for apples.

5. Chlor–fenvinphos – Seed treatment and soil application.

6. Confidor – Systemic, contact and stomach poison.

7. Cupermethrin/ – Non systemic, contact and stomach poison.Cypermethrin

8. Cupric acetate – Fungicide and insecticide.

9. Diazivon (liquid) –

10. Imidazole – Fabric eating pests and contact poison.

11. Ethion – Cattle lice abatement, non systemic insecticide for citrus,decidous fruits, cotton and ornamental plants.

12. Kafil – Smoke insecticide (closed space) for white fly,cockroaches and domestic insects.

13. Oxytheoate – Systemic, with contact stomach poison and alsospidermite. For fruits and vegetable.

14. Propoxur – Nonsystemic, for action on sucking and biting insects(aphids, mealy bugs, leaf hoppers, caterpiller on cocoa,rice, oil Palms and others.

15. Rampant – Soil applied for seedling pests and cabbage.

16. Reldon–50 – Organophosphate insecticide for stored grain and rape seeds.

17. Terbufo S – Soil insecticide for vegetable and food crops and nematicidewith stomach and contact poison.

18. Terraour P – Nematicide and soil dweling insects.

19. Terrathinon – Organophosphorous insecticide.

20. Endosulfan/Thioclan – For control of sucking, chewing and boring insects and(liquid) mites in a wide variety of crops.

21. Thripstick – Pyrethroid insecticide-non systemic for control of manycrops.

22. Dichlorovas/Vapona –

23. Volathion – Foliage and soil application for control of lepido-plerouslarvae, bettles and its larvae and locust on large variety ofcrops.

24. Zind – Fungi in fruits and vegetables and ornamental trees.

25. Zolone – Organophosphrous insecticide – for insects and spiderson fruits and vegetables.

26. Deltamethrin – For mosquito killing.

27. B.H.C. – Insecticide

28. DDT – Used in public health sanitation

29. Methyl parathion –

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246 REFERENCE BOOK ON CHEMICAL ENGINEERING

30. Monochrotophos (liquid)

31. DDVP (Dichlorovos) – Liquid

32. Diuron

33. Canbaryl/Sevin – DDT equivalent

34. Dimethoate –

35. Meta sytox –

36. Al phosphide –

37. Zinc phosphide –

38. Phorate –

39. Chlorobenzilate

40. Cupric pyriphosphate –

41. Butachlor – Liquid

42. Data pon –

43. TEPP –

44. Lindane (Y BHC)

45. Thiram

46. Fenthion

47. Endosulphun

48. Pyrethrun extract

49. Quinal phos

50. Aldrin – For soil bound pests (termites, cut worms, grass hoppersetc.). Contact and stomach poison – used as dust spray,WDP.

51. Warfarin – Safer insecticide.

52. Clordane – For crickets, locusts, cockroches, ants and leaf eatinginsects.

53. Nicotine sulphate – Plant insecticide active component containing (0.5%)

54. Nim oil – Vegetable tree origin active component (0.5%)

55. Methoxyclor – Safe for plants.

56. Chloropyriphos –

57. B.T. – Bio insecticide.

58. Datopon –

59. Allethrin – Mosquito repellant

60. Malthion –

61. Phosphomidon –

62. Deltamethrin – Mosquito killer

63. Prallethrin – Mosquito killer.

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INSECTICIDE OR PESTICIDE 247

2.3 Group C – Molluscicides1. Calcium arsenate

2. Melaldehyde

3. Clonitritide

4. Methio-can

5. Mini Slugit pellets

2.4 Group D – Fumigants1. Al phosphide

2. Ethylene dibromide/dichloride.

3. Ethylene oxide gas (B.P. 12°C) – Cereals, empty building and plant disinfection.

4. Tetrachloromethane – Green house fumigant

2.5 Group E – Fungicides1. Copper oxychloride

2. Aaterra W P – Soil based or compost

3. Acticide PMA 100 – Has herbicide action also.

4. Afugan

5. Aliette – For horticulture crop

6. Anildazine – Nonsystemic, foliar aplication for potato, tomatoes andleaf spot.

7. Antifungin –

8. Arsenic trioxide –

9. Akiran – For cereals, rice, cotton and vegetables.

10. Ashlade TCNB – Additionally potato sprouting prevention.

11. Bitertanvol – Control of scab on appel and black spot on roses.

12. Butyl Paraben – Food preservation and in pharma control of powderymildew.

13. CaO –

14. Calixin – For cereals and vegetables.

15. Captafol –

16. Carbendazim – For wide variety of cereals, fruits and vegetables.

17. Carboxin – For cereals.

18. Chlorothalonil – Non systemic, wide variety of crop and additives formarine coating.

19. Mancozeb –

20. Nickel chloride –

21. Sulphur (Collidal) – WDP and Dust.

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248 REFERENCE BOOK ON CHEMICAL ENGINEERING

22. Thiram

23. Zineb

24. Ziram

25. Aurcofungin –

26. Ferbam –

27. Copper (++) hydroxide –

28. Dichlorophen – Moss controlling

29. Diphenyl –

30. Folicor –

31. Fera thinosulf – Soil fungi-cide.

32. Carbendazim –

33. 40% formaldehydesolution with water – Soil fumigation

2.6 Group F – Herbicides1. Acifluorfen (LD50 = 1300 mg/kg)

2. Agriphalan –

3. Alachlor (LD50 = 1200 mg/kg)

4. Amcide –

5. Arsenic trioxide (LD50 = 1.46 mg/kg)

6. Aresin (LD50 = 1660 mg/kg)

7. Atrazin (LD50 = 1100 mg/kg)

8. Benzolin (LD50 = 4800 mg/kg)

9. Benlazon –

10. Bifenthrin (LD50 = 1740 mg/kg)

11. Chloroxuron (LD50 = 3700 mg/kg)

12. Datapon (LD50 = (7126 mg/kg) – For control of grass in crop

13. Diuron – – For control of weeds in non crop area.

14. Dowpon (LD50 = 9330 mg/kg) – For control of weeds and mosses in non-crop areas viz rail roads and rubberplantations.

15. Butachlor –

16. Isoproturon –

17. Paraquat dichloride –

18. Granoxone –

19. Fluroxypyr – Broad leaf weeds.

20. MEPA –

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INSECTICIDE OR PESTICIDE 249

21. Propanil –

22. Benzonitrates –

2.7 Group G – Slimicides1. Dodecyl Dimonium chloride – For swiming pool and water treatment plant.

2. Drewbrom –

3. Vanicide – For petrol tanks, C.W. basins, paper plants and cottonfabrics.

4. Mycocide –

2.8 Group H – Rodenticides1. Barium carbonate (15–20%) –

2. Comafuryl –

3. Zinc. Phosphide –

4. Alpha Chloralose –

5. Bromediolone –

6. Cupric arsenite –

7. Difenacoum –

8. Drat –

9. Killgerm, Sewarin –

10. Malla – dnite. –

11. Phostoxin –

12. Photo phor –

13. Hydrocyanic acid (prusic acid)–

14. Racumin –

15. Warfarin – 3 –

16. Thallium Sulphates –

17. Aldichlor –

18. Arsenic oxide. –

2.9 Group I – Nemoticides1. Chloropicrin –

2. Cloetho carb –

3. Etho prophos –

4. DCIP –

5. 1, 3 dichloropropane – Has fumigant action to control nematodes.

6. Dizomel –

7. Fenamiphos –

8. Fensulphothrin – Soil application.

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250 REFERENCE BOOK ON CHEMICAL ENGINEERING

9. Iozofos – Root nematodes control in rice, maize, sugar and vegetables.

10. Phorate – For sour fruits, vegetables, and grain

11. Oxamyl – For fruit trees, vegetables, beat and bananas.

12. Triazophos – For straw-berries, tulips and garlic.

13. CS2

14. Carbofuran –

N.B. Banned pesticides are Aldrin, Chlordane, DDT, Heptachlorendin, Taxo-phane anddibromopropane. DDT can be used for public health only. Pesticide act does not enlist all the modernpesticides listed above.

The unit of toxicity of pesticides is usually expressed as LD50 which means, it is lethal to 50%of test animals, followed by the dose expressed as mg/kg body weight. The test animals are usuallyrats and oral (orl.) dose is given. Example LD50 = 1100 mg/kg for Atrazin (herbicides).

3. Pesticides are complex organic molecules, usually chlorinated hydrocarbons and organophosphorus compounds which are more toxic than carbamates. There are some inorganicpesticides also usually of copper, arsenic, barium and calcium compounds. There are someplant based insecticides, viz neem (margosa) oil from neem seeds, kernel and leaves contg.active component, Azadiractin Indica and ether extract of which (1.5%) is very effectiveagainst locust and white cotton fly. Plant based insidcides are biodegradeable and insects donot develop resistance to the insecticide. The residue, neem cake after neem oil extraction, isused as a bio fertilizer.

Emulsifiable concentrate is one liquid, dispersed in another liquid, each maintaining its originalidentity and the two liquids are prevented from reacting with each other by the addition of anemulsifier. Emulsions are milky. Herbicides are generally soluble in water. There are powderinsecticides also.

4. SOLVENTS FOR PESTICIDES/INSECTICIDESFor application of pesticides, not soluble in water , or plants, crops etc. To form a water

system, it requires the use of an emulsifier (nonionic, cationic/anionic, inorganic and natural). Exceptinorganic emulsifier, all other types of emulsifiers are biodegradeable.

An emulsifer (surface active agent) is having a chemical structure in which the molecule isdivided into two moieties–one part of which is hydrophilic (water soluble) and the other part ishydrophobic (water insoluble), usually hydrophobic part is soluble in organic solvents. Emulsifereffects wettability by influenoing both surface tension and contact angle. For longer storage ofpesticides, stability of emulsifier is important. Emulsifier pesticides are important because of beingmore biologically effective and application is easier and economic. Other dispersal system are alsoused. Wet-able pesticides powder also contain surface active agents.

The emulsifier molecule's hydrophobic moiety is always nonpoliar alephatic and/or aromatichydrocarbons group, where as the hydrophilic section contents either an ionic group or an accumulationof OH– group or a poly (Alkenyl Oxide) group e.g., (–CH2 – CH2 – O –)n. The emulsifiers in thefirst group above are called anionic surfactants and the second group is called polar surfactants.Classification is determined based on whether the main moiety that is left behind after disolution, isnegatively charged or positively charged.

Emulsifiers are numbered with a prefix alphabet denoting the type.

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INSECTICIDE OR PESTICIDE 251

Table 1

Nonionic emulsifiersAliphatic alcohols (–COO) Sorbitol

Ethylene Glycol (–COOCH2CH2OH) Penta erithritol

Polyethylene glycol Saccharose

Polypropylene glycol Polyglycol ethers.

Glycerol/Polyglycerol Condensed Phenols

Table 2

Cationic emulsifiers

Fatty amine salts,

Salts of alkaline diamine, e.g., alkyl benzyl ammonium

Salts of alkaline, Polyamines

Table 3

Anionic emulsifiers

Alkyl Carboxylates

Alkyl Sulphonates

Alkyl Benzene Sulphonates (Sparingly soluble)

Sulphated alkylamides

Phosphates of phenols

Organic compounds of H3PO4

Table 4

Solid Inorganic emulsifier

Bentonite

Fuller's earth (non plastic clay mainly mineral montrorillo nitrite)

Aluminium salts

Ferric hydroxide

Water glass.

Natural emulsifier (Partially surface active lanolin)

Egg Yolk (cholesterols), Gelatine and casin.

Additives (Promoters) for pesticides : Aliphatic alcohols (2-ethylhexanol), urea and xylene.

Emulsion preservatives – Glyoxal (not biodegradable). Emulsion stabilisers – polyglycol, ethersof alcohols, fatty acids, glycerides and alkyl phenols.

5. CRITERIA OF SELECTION SPECIFIC EMULSIFIER FOR A PESTICIDE(i) Solubility: Emulsifier should be sparingly soluble in internal phase and soluble as in external

phase oil. Soluble emulsifiers form w/o emulsions and water soluble emulsifiers tend to form o/wemulsions as per Bancroft rule.

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252 REFERENCE BOOK ON CHEMICAL ENGINEERING

(ii ) Chemical Structure: It should match the chemical structure of internal phase (similarchemical structure of pesticide desirable).

(iii ) Phase volume ratio: It determines the external phase type of emulsion. Excess of oilproceduces w/o (water in oil) emulsion which requires oil soluble emulsifiers; With excess of water,o/w (oil in water) emulsion is produced for which water soluble emulsifier is used.

(iv) Nonionic emulsifiers are required for preparation of w/o emulsion. Addition of anionicemulsifiers gives rise to mixed emulsifiers which are widespread in use.

(v) H.L.B. values: Emulsions are prepared with either one, two or more emulsifiers, usuallywith different H.L.B. value (hydrophilic – lipophilic balance). Hydrophilic emulsifiers with high H.L.Bvalue, gives formation of o/w emulsion. On the other hand, hydrophobic emulsion, with low H.L.B.value, are more used for preparation of w/o emulsions. H.L.B. values of emulsifiers are given intable-below

Table 5H.L.B. value of emulsifiers (non ionic)

Fatty Acid esters of H.L.B. valueEthylene glycol 1.5–2.9Polyethylene glycol 1.8–18Glycerol and polyglycol 0.8–4.5Sorbitol 1.8–8.6Saccharose 7–15Polyglycol ethers ofAlcohols 8.2–16.9Fatty Acids 8.1–15Glycerides 8.0–18Alkil Phenols 9.92–16.5

Trial and error: Based on above stipulations, one/more emulsifiers are selected and a trial sampleof emulsifiers with particulars of pesticide is selected for further test. Quantity of solvent (emulsifierand others if any) varies from type of pesticides emulsion. The following table gives the percentageof solvents required for liquid pesticides.

Table 6

Pesticides Solvent % wt.Endosulfan, 35%E. C. 62Butachlor 44DDVP, 76% 16Monocrotophos W.S.C. 48

6. WOOD INSECTSCommon insects, which destroy wood, are termed as termites and wood worms (Arobium

pumctalum, teredo, long worm banberia, monteria beetle, lyctus and xeslabium and rufovillo – san).

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INSECTICIDE OR PESTICIDE 253

7. MANUFACTURE OF NEEM BASED PESTICIDESA. Neem seeds are crushed and extracted by Soxhlet extraction using petroleum ether. The

extract is concentrated to yield paste type residue which is then mixed with more ether. Oil is keptfor about a month when fatty solid matter settles down and separated by decantation. The yellowcoloured liquid is called Neem oil or neemol. Neemol protects about 94.7% of leaf area at concentrationof 1000 ppm.

B. For Nimidin manufacture, crushed seed of neem, and ethyl alcohol are used in Soxhtletextractor which yields vermidin. It is then mixed with ethyl acetate and water. The ethyl acetatesoluble part is then concentrated and the resultant residue is again partitioned between a mixture ofpetroleum ether and aqua methanol soln (5:95). The aqua methanol soln. is concentrated to get brownsemisolid residue called Nimidin. The solid residue obtained from both of these processes is usedas organic manure.

Page 265: Reference Book on Chemical Engineering v. 1

It is a systematic procedure in Industrial engineering for scheduling and managing complicatedprojects. The basic factors for CPM are.

(i) A large project consists of a long list of smaller tasks.

(ii ) Some of these tasks are of such nature that the next task cannot be done unless some otherone is finished.

(iii ) The manpower available at any given period is limited.

(iv) A careful planning can device a system of priorities which ensures that most importanttask is always being worked upon by the largest number of people of the project. The manpowerdeployed will be as uniform as possible.

(v) The sequence of tasks which is done at least time period one after another without anyinteruption is the critical path.

(vi) The procedure is set in diagram depicting all tasks with time periods for completion, floatsif any etc. The shortest route time period for completion of the project is called the critical path forthe project scheduling. The CPM chart is made with the aid of a computer.

N.B. PERT – Evaluation and Reviewing

Technique It is slightly different from CPM technique.

CRITICAL PATH METHOD (CPM)

Chapter

43

254

Page 266: Reference Book on Chemical Engineering v. 1

PSYCHROMETRY

Chapter

44The properties of moist air viz. humidity, relative humidity, wet bulb temperature, enthalpy,

humid vol. and saturated volume are dealt in psychrometry. In humidification, evaporation of wateror other liq. takes place in contact with air and dehudification means condensation of water in airwater mixture or a mixture of non condensible gas and a liquid. Specific humidity of an air watermixture is the lb/kg of water vapour carried by l lb/ 1 kg of dry air and it is dependant on partialpressure of vapour.

Percentage humidity is the ratio of actual humidity to the saturation humidity at the air/gastemperature. At all humidities except 0 and 100 percent, the percentage humidity is less than relativehumidity. Percentage R.H. is the ratio of partial pressure of water vapour in air water mixture atexisting temperature to the vapour pressure of water at dry bulb temperature. Dew point temp is thetemp at which a given mixture of air and water) (or a non condensing gas and a liquid) is cooledat, constant humidity, to become saturated. It is also called adiabatic saturation temperature. Totalenthalpy is the heat content of air water or gas–liquid mixture. Wet bulb temperature is the equilibriumtemp. attained by a water surface in contact with air (or a non condensing gas) such that the latentheat of evaporation of water or liquid in the interface is equal to sensible heat transferred from airwater mixture to the water surface. Dry bulb temperature is the ambient temperature. The differencebetween D.B. temperature and W.B temperature is called wet bulb depression.

Humid volume is the total volume of a unit mass of vapour free gas and that of water vapourin it at 1 atm and existing temperature of gas. For a saturated gas, humid volume is saturated volume.From psychrometric chart (Fig.1), humidity, enthalpy, dew point, D.B./W.B. temperatures, enthalpyetc., can be found when any two of above factors are known. Humid heat is the heat necessaryto increase the temperature of 1 lb or 1 kg of gas and vapour it may contain in it by 1°F or 1°C.

Moisture content of air and its temperature is not only important for human comfort but alsoin industry for processing and storage of various products including food and some pharma productsand is the basis of air conditioning. In the process of humidification, cooling of liquid takes placedue to evaporation and this principle is used in cooling towers.

Calculation of various properties of air can be made when some factors are known.

Wet bulb temperature

( )w fg w

kwt t h w w

hfg′= − × −

255

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256 REFERENCE BOOK ON CHEMICAL ENGINEERING

Fig. 1 Psychrometric chart at atmospheric pressure.

G rain s of M o isture pe r lb o f d ry a ir.

Loss of w ate r per lb o f dry a ir.

2530

35

4045

5055

6065

7075

8085

9095

100105

110 20 30 40 50 60 70 80 90 100

110

120

130

140

150

160

170

1800.0

25

0.024

0.023

0.022

0.021

0.020

0.019

0.018

0.017

0.016

0.015

0.014

0.013

0.012

0.011

0.010

0.009

0.008

0.007

0.006

0.005

0.004

0.003

0.002

0.001

0.000

For barom

etric Pressure o

f29

.92 ln Hg

Dry B

lub Tempera

ture—D

eg FB

arometric pre

ssure. 29.92 in of Hg

Source: P

erry's Hand book 3rd

edn. 1949

Entha lpy a t sa tura tion B .t.u . pe r pound of d ry a ir

100

2530

35

40

45

50

55

60

65

70

8 0%70%

60%50%

30%

20%

10%

75

80

1 0.1 Btu

02

0305

13 .0 cuft

– .005 b tu

13 .5 cu ft

–0 .01 b tu

Wet bulb tem

perature

0 .03 B tu

14 .5 cuft lb o f dry a ir

0 .02 Entharpy devia tion B tu per lb o f d ry a ir

4846

44

42

40

39

38

34

32

30

2826

22 24

2018

16

14

12

40% Relative hum

idity

W et bu lba nd de w p o in t

o r sa tura tio n te m p eratu re

32

1.0

0.8

0.6

0.2

40

Tempe

rature of w

ater addedo

r rejected deg F

50

6070

80

1601208020

0

Enthap

y of wa

terper lb

of dry air

12 .5 cuft

04

Gra ins o f m

o is tu re pe r

16 d ry air

Page 268: Reference Book on Chemical Engineering v. 1

PSYCHROMETRY 257

where t = D.B. temp °C

tw = wet bulb temp °C

kw = diffusion co-eff. of water vapour through film of air water vapour mixture, kg/m2

′h f g = Enthalpy of vaporisation at wet bulb temperature kcal/kg

hfg = Enthalpy of vaporisation at dry bulb temperature kcal/kg

ww = Specific humidity at wet bulb temp.

w = Specific humidity at dry bulb temp.

If the coefficient, kw is not known, dew point can also be calculated as per the modifiedA.P. Jhon equation or carrier equation.

Specific humidity

w = M P P18.016

M P 28.966 Pv v v

a a a

= × or 0.622 P

Pv

a

where, w = specific humidity

Pv = partial pressure of moist air, mm Hg

Pa = partial pressure of dry air, mm Hg

Mv, Ma = Mol. wts of water and air respectively

Dew Point

Modified A.P. Jhon equation for dew point temp. calculation

Pv = ( )1.8P

P2700

wv

t t′

−−

where, Pv′ = satn. press. at wet bulb temp, mm Hg

Pv = partial pressure of water vapour in air, mm Hg

t = D.B. temp °C

tw = wet. bulb temp °C

P = total pressure (Pair + Pv), mm Hg

Carrier equation for dew point calculation

Pv = ( ) ( )

( )P P 1.8

P2800 1.3 1.80 32

v wv

t t

t′

′− − ×

−− +

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258 REFERENCE BOOK ON CHEMICAL ENGINEERING

A. CLASSIFICATIONGlass Type Uses

E Glass – Alumino borosilicate For GRP and including

glass containing alkali use in other appliances.

1% (wt)

C Glass – Alkali–lime glass with High acid resistance

high borontrioxide appliances use and

(B2O3) staple fibres.

A Glass – Alkali–lime glass with Spl. applications/acid

little or no B2O3 and resistant, and cement

alkali 1%(wt) reinforcement.

E–CR Glass – Alumino–lime silicate For G R P and flue

glass with alkali 1%. gases pipes.

High acid resistant

R Glass – Alumino–silicate glass Spl. use in G R P

without Ca and Mg oxides– boats of high power.

high much properties.

D Glass – Borosilicate glass-speciality Micro wave heating

glass with high plates and special uses.

dielectric properties.

S Glass – Alumino silicate glass Used in G R P boats of

with MgO = 10% good high power.

tensile strength.

GLASSES AND TEXTILEGLASS FIBRES

Chapter

45

258

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GLASSES AND TEXTILE GLASS FIBRES 259

B. DIELECTRIC CONSTANTS OF TEXTILE GLASSES AT 1 MH Z

E glass = 5.8 – 6.4

C glass = 6.8

E–CR glass = 7

R glass = 5.6 – 6.2

S glass = 4.8 – 8.3

D glass = 3.85

Quartz glass =3.78

C. TEXTILE GLASS FIBRES ARE MADE FROM DIFFERENT GLASSES AS ABOVEBY FIBERISATION PROCESS DESCRIBED IN CHAPTER 26

N.B. 1. Glass filament yarn – ISO – 2078 and ISO 3599 EC–9–34 where E glass and C glasscontain 9 filament diametres in µm

2. 34 tex (1 tex = 1gm/1000m)

D. USES OF TEXTILE GLASS FIBRESTextile glass fibres of different glasses is available as glass filament and glass staple fibres of

limited length (spun fibres) of dia. 9 – 13 µm. Uses involve insulation, textile purposes viz decoration,filtration, reinforcement of a matrix to make a composite. Matrix can be plastics (thermo or thermosets),bitumen, rubber, cement, gypsum and other materials.

Textile yarns and plied yarns with filament dia of 5–13 µm are mostly woven into fabrics. Theplastic admix products viz mats, rovings etc are made from glass filaments of 9–24 µm dia. Tensilestrength of E glass filament = 3400.Mpa and that of R glass filament is 4400 Mpa.

E. COMPOSITION OF GLASSES

Multi– A glass C glass E–CR Alkali R S Dpurpose glass resistance Glass Glass Glass

glass

SiO2 53–55 70 – 72 60–65 58 60 60 60–65 73–74

Al2O3 14–15.5 0 – 2.5 2–5.5 12–13 0.7 24.5 20–25 –

CaO 20–25 5 – 9 14 21 5 6 – 0.5–0.6

MgO 20–25 1 – 4 1–3 4.5 – 9 10 –

B2O3 6.5–9 0 – 0.5 2–7 <0.1 – – 0–1.2 20–23

F 0–0.07 0.15

Na2O

ZrO2 <1 1 0.4 0.1

K2O 0.3

Fe2O3 2.1

TiO2

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260 REFERENCE BOOK ON CHEMICAL ENGINEERING

ENVIRONMENT AND POLLUTIONAIR AND WATER

Chapter

46

1. SOLAR ENERGYAbout 20% of total solar energy transmitted by sun is lost through space until it reaches about

3–5 km above a city. A polluted city atmosphere can reduce further about 10–20% of sun's energyout of 80% reaching on the earth. The solar energy thus reaching is sufficient to initiate photochemicalprocess resulting in smog formation due to complex reactions between oxides of nitrogen andhydrocarbons present in city air in presence of solar radiation.

The remaining solar energy (short wave radiation) is then absorbed by the earth's surface andre–emitted as long wave or heat wave radiation. The air layers, close to the radiating surface, soil,building structures or any other objects, are heated and start to rise as convection air stream. Theair motion thus produced will disperse and dilute air pollutants. The two metrological phenomena,responsible for high or low pollutants levels in air, are due to atmospheric stability and air flow isdetermined by sun's energy reaching the earth.

1.1 Atmospheric StabilityThe ground surface heating and resulting in heating of air adjacent to it, produces change in

temperature with height above sea level which is called adiabatic lapse rate @ 5–4 °F per 1000 ft.When the temp. decreases with height, the lapse rate is +ve and a good dispersion and verticaltransport of pollulants can be expected under this unstable weather condition; conversely, the air isstable when the adiabatic lapse rate is –ve when the air temperature increases with height. Whenlapse rate becomes –ve it is also called an inversion and under this condition no vertical dispersionof pollutant in air can take place and thus the pollutants remain trapped within the inversion layerof air at the particular ht. In table 1 temperature above sea level at different zones are given.

1.2 Greenhouse EffectEarth atmosphere act as a greenhouse in trapping heat from sun after it is reflected from earth

surface as a long wave (infra red) radiation. The absorption of long wave is effected by smallamounts of water vapour. CO2 and ozone gases are called greenhouse gases in the air. The cloudsare opaque to too long wave radiation unless they are extremely thin and cirrous clouds, after clearsky can increase surface air temp. by a few degrees. The green house gases affect the surface airtemperature which causes unstable weather condition. The burning of fossil fuels, auto emission, andother combustions increase the CO2 conc. in air. Under Kyoto Protocol (1997), six greenhouse gases

260

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ENVIRONMENT AND POLLUTION AIR AND WATER 261

have been identified which are, a part from CO2, CH4, Nitrous oxide, HICs, CFCs and Sulphurhexafluoride. Also ozone layer over earth atmosphere if broken by greenhouse gases, the naturalprotection against ultraviolet rays is removed which pass through ozone hole. This causes moreincrease in air temperature with the possibility of more melting of ice and increase in sea water level.

1.3 Composition of Clean Dry Air at Sea LevelN2 = 78% vol.

O2 = 20.94

Argon = 0.93

CO2 = 318 ppm

Neon = 18 ppm

H2 = 0.5–1 ppm

CO = 0.1 ppm

CH4 = 1.5 ppm

Ozone = 0.02 ppm

SO2 = 0.0002 ppm

NOx = 0.001 ppm

2. METHODS OF CONTROL OF LIQUID EFFLUENTS FROM INDUSTRYThere are three main methods of handling liquid effluents.

(i) Chemical treatments

(ii ) Mechanical treatments

(iii ) Biological treatments

These methods are further subdivided into following categories of treatments :

(a) Various chemical treatment methods available.

(b) Biological treatment to reduce BOD. A high CODBOD

ratio indicates that the effluents

are not biodegradable which can not be converted to biodegradable even by bacteria.

(c) Air filtration/ pressure filtration

(d) Sedimentation in clarifiers with coagulating agents.

(e) Forced aeration by aerators in lagoons.

(f) Pure oxygen activated sludge process or wet oxidation process.

(g) Activated sludge cum carbon activated process.

(h) Electrodialysis

(i) Semipermeable membrane process.

(j) Dissolved air flotation process.

(k) Biotechnology method.

(l) Anarobic fermentation process using microorganism (bacterial strains)

(m) Ion exchangers

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262 REFERENCE BOOK ON CHEMICAL ENGINEERING

(n) Flocculators

(o) Floating aeration in ponds

(p) Storage of treated effluents in delay ponds (1+1) and slow discharge to outfall throughstorm water drains.

(q) Molten Metal Technology.

2.1 Biological Treatment Methods(i) Special bacteriological strains/cultures (viz thermobac, polybac) which can make metabolic

conversion of poisonous into non-poisonous materials. The cultures are available for HCN, nitrite,Phenolics, aldehydes, petroleum oils and other organic toxic materials.

(ii ) Pure oxygen activated sludge can simultaneously cause biodegradation and chemical

conversion of wastes containing high CODBOD

ratio.

(iii ) Wet oxygen process can destroy wastes from too dilute a stream for incineration and tooconcentrated effluent for conventional treatment.

(iv) Activated sludge cum activated carbon process can handle wastes, containing bothbiodegradeable materials and wastes, having very high chemicals.

(v) Ion exchange and electrodialysis methods are for removal of ionic wastes.

(vi) Dissolved air floatation process for removal of oil and emulsion wastes. Fine air bubblesare sparged at the bottom of wastes which carry both oil and emulsions to top as scum which areperiodically removed. Efficiency is over 95%. Suitable also for fine solids and colloids.

(vii ) In biotechnology method high and low toxic materials from pesticide units are separatelystored in polythene lined solar evaporation pond. Sun’s rays evaporate water from high and low toxictanks. In the high toxic tanks, on concentration, the pollutants become harmless. The technique isnot very convincing. This process is usually used in pesticide plant wastes. The water from pesticidefree tank can be used for land fill after neutralisation with lime, aeration and flocculation. The lowconcentrated pond similarly gets pollutant free or the pollutants within limit.

(viii ) Floating aeration in lagoons–The process has several floating aerators in lagoons, handlingobnoxious wastes, usually from paper mill, after lime dosing. Oxygen is supplied to wastes byaereators.

(ix) Anaerobic fermentation of brewery/distillery wastes, containing alcohol are usually carriedout by methanococcus bacteria in a closed fermenter when alcohol is degraded by bacteria to CH4and CO2 gases which can be used for fuel purpose in the plant.

Methane bacteria has 9 types of strains, each for different substrates (food for bacteria).Sewage sludge can also be digested by anaerobic treatment.

According to Barker, the 9 strains of methane bacteria are as follows.

Products

(a) Methanobacterium formicicum – Formate, CO2 and H2

(b) – Do – meliaanski – Primary and secondary alcohols, H2

(c) – Do – propionicum – Propionate salt.

(d) – Do – Sohngenii – Acetate and butyrate

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ENVIRONMENT AND POLLUTION AIR AND WATER 263

(e) – Do – Suboxydans – Butyrate, Valerate

(f) Methanococcus mazei – Acetate, butyrate

(g) – Do – Vanielli – Formate, H2.

(h) Methanosancina methanica

(x) Molten Metal TechnologyThis was developed in USA. The process disintegrates hazardous wastes into elemental form

in a hermitically sealed unit when wastes are separated into elemental from which can be convertedto useful by products. The details are not available.

(xi ) Solid Wastes DisposalA. Hazardous solids are disposed of by putting in sealed drums which are dumped in concrete

underground tanks.

B. Overground dumping of hazardous wastes on concrete floors.

C. Sedimentation in ponds/lagoons

D. Incineration–mainly for hospital garbage and domestic refuge.

E. Chemical treatment method.

Stipulation of Hazardous wastes, limits of hazardous wastes generation and disposal methodsare elaborated in statutory Hazardous wastes (management and handling) Act 1989. Radio activewastes are covered under Atomic energy Act 1962.

Water pollution from industrial effluents are covered under the water (prevention and control)of pollution Act, 1974. Disposal of treated industrial effluents are also controlled by MINAS or StatePollution control board standards.

In table 2 limits of pollutants as per MINAS/ IS 2490/Assam pollution control board (forNamrup fertiliser plant) for final discharge of effluents to river is given.

3. WASTE WATER STREAMSFrom large chemical processing plants can be grouped as follows(a) Chemical effluents sewers from process plants

(b) Oil water effluent sewers from compressors.

(c) Cooling water purge sewers.

(d) Steam–water sewers from plant sewers.

(e) Water treatment plant sludge disposal sewer.

(f) Sanitary sewers.

(g) Solid wastes disposal.

3 (a) Chemical Effluent SewersThe sewers from process plants should be designed to collect contaminated process chemicals

wastes which occur as discharges from process equipment, leakages from pumps glands, spillagesand floor washings. These are separately collected in a pumping pit in the plant through separatelines and from where it is pumped through a properly designed pipe line to effluent treatment plant,designed for treatment of such effluents. In case of ammonical effluents, it is stripped with L.P.

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264 REFERENCE BOOK ON CHEMICAL ENGINEERING

steam when ammonia is removed. The remaining ammonia in stripper outlet water is air stripped ina cooling tower and effluent discharged to delay pond.

Storm water from trenches in the plant goes directly to storm water drains along plant roadsas it does not contain any harmful chemical effluent. Acidic and alkaline effluent from D.M. plantare mixed in a pond within the plant B.L and pumped to chromate treatment plant or delay pond.The D.M. plant pond is usually rubber lined and D.M plant floor area, trenches are lined with acidproof tiles.

3 (b) Oil Water Effluent Sewers

The oil water effluent from compressors in a plant, coming through sewers, are usually treatedat the API oil trap, containing coke and clear water is discharged into the storm water drains. Theoperation of oil traps is to be regularly monitored for performance.

3 (c) Purge Cooling Water SewerThe cooling water is usually treated in chromate treatment plant and contains 10 : 20 ppm of

chromate CrO4 = (+6) and phosphate (TSP) to prevent corrosion of C.W pipelines and equipmentusing cooling water. Cr(+6) is to be reduced to Cr(+3) before discharge. The purge water from eachcooling tower is led into a sewer pipe which flows to adjacent purge cooling water treatment plantusing 10% Sodium meta bisulphite solution after C.W is acidified to pH 2.5 and treated with Sod.meta bisulphite, NaHSO3 which reduces Cr(+6) to (Cr+3).

H2SO4 + NaHSO3 + Na2Cr2O7 → Na2SO4 + Cr2(SO4)3 + 2NaHSO4

The reaction mass from Sodium meta bisulphite reaction tank, having agitator is transferred toneutraliser, where it is treated with lime solution and pH is brought upto 7.5. Acidic and Alkalinemixed effluent water from DM plant can be mixed here also. The neutrlised effluent is then pumpedthrough sewer line to delay ponds from where it is discharged to treated effluent discharge drainthrough delay pond overflow point.

3 (d) Steam Condensate Sewer from PlantsThe condensate blowdown from boilers are collected in separate sewers as it contains alkaline

wastes and pumped from plants to delay pond.

3 (e) Water Treatment Plant (WTP) Sludge DisposalThe sludge, containing 3–5% suspended solid from water treatment plant, usually contains

Ca(OH)2,CaCO3,A1(OH)3, mud etc. and is drained by pumping to sludge settling tank when suspendedmaterials settle at the bottom and clear water is discharged to final effluent drain of delay pond.

3 (f) Sanitary Sewers Effluent TreatmentThe effluents from septic tanks are taken by 4" lines and combined with other sewer lines to

a 8" sewer line and the sewage taken to septic (treatment) plant. usually, a small concrete pit with(+) 6" seal between inlet and outlet sewer lines is provided at direction change points of sewer lines.The pit is covered with concrete grills at top.

3 (g) Solid Wastes Disposal(i) For hazardous solid wastes, packing etc. are usually put in plastic or metal drums and

lids are sealed. The drums are put in underground concreate bunkers and entrance is covered withconcrete slabs.

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ENVIRONMENT AND POLLUTION AIR AND WATER 265

(ii ) For other solid wastes, like catalysts containing harmful metal salts etc, are dumped incovered rooms with concrete floor for long storage and if possible, sold to interested parties.

4. SURFACE WATER THROUGH STORM WATER DRAINSDepending on total area of plant, the run–off water rates from rains are calculated as follows.

(i) Run–off water as 100% for all paved area inside the plant.

(ii ) Run–off water as 50% for unpaved areas inside the plant–the other 50% is thought tohave been absorbed in other soil. Rain water from individual plants are discharged to storm water drains.

(iii ) Rain water accumulation per inch of rainfall per hour per ft2 area is 0.014 US gallonsper minute (0.0539 lit/min per ft2). In addition consider fire water accumulation of 500 US gallonsper minute for reasonable duration and any other uncontaminated water quality which comes fromplant to storm water drains which ultimately goes to outfall points along with delay ponds over flow.W.T.P. plant sludge water quantity and individual effluent treatment plant’s treated effluent quantityalso goes to outfall point.

5. OTHER EFFLUENT TREATMENT PROCESSES FOR SOME INDUSTRIES5.1 Fertiliser Plant Chemical Effluents5.1.1 Urea Plant

The plant generates (a) Vacuum condensate from Vacuum concentrators containing urea andNH3 from prilling tower top where the vacuum concentrators are located. The condensate is treatedin urea hydrolyser when urea hydrolyses to NH3 and CO2.

NH2CONH2 + H2O → 2NH3 + CO2

The vacuum condensate is to be first stripped in upper stripper column containing bubble capplates after preheating to 110°C and taken out from bottom of upper section and fed to ureahydrolyser after preheating to 189°C in feed preheater. Hydrolysis is carried out at 18 ata and 195°Cby indirect steam heating in inbuilt steam heater bundle.

The hydrolysed solution from urea hydrolyser is then fed to bottom section of NH3 stripperwith a kettle type reboiler at bottom using 6 ata steam and NH3 and CO2 recovered are recycled toprocess. The Conc. of urea reduces from 0.84% to 380 ppm and that of NH3 Conc. reduces from3.82% to 140 ppm. The treated effluent from stripper bottom is stored in a 500m3 undergroundstorage tank along with pump spillages and from there it is pumped to a 500m3 underground storagetank for air stripping of ammonia after it is made alkaline by adding NaOH solution and pH raisedto 9. The stripped solution at bottom of air stripper may contain upto 30 ppm ammonia which isthen sent to delay pond for slow discharge.

5.1.2 Ammonia Plant (NG based)

5.1.3 The process condensate, generated in purification section contains NH3, CO2 etc and is strippedin a L.P steam stripper. The condensate contains 500 ppm NH3, 4000 ppm CO2 and 1500ppm methanol. The condensate is flashed in flash vessel when most of the CO2 is removedand then stripped to remove NH3 and methanol. The stripped condensate contain NH3 = 10ppm, CO2 = 10 ppm and 20 ppm methanol which is sent to D M plant for cation polishing.

The purge water from the recovery section of ammonia plant, containing 1% ammonia, is sentto 500 m3 underground effluent storage tank in urea plant. In Table 2, the analysis of waste water

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266 REFERENCE BOOK ON CHEMICAL ENGINEERING

standards for discharge to Rivers, canal, etc is given for fertilizer plant manufacturing urea andintermediate product of NH3.

5.1.4 D.M. PlantThe acidic effluent, generated by cation exchanger condensate polishing unit, is to be taken to

D M plant neutralisation tank with rubber lined and with epoxy coating. Similarly, alkaline anionexchanger effluent and process water gravity filters are to be taken to neutralisation tank where pHis neutralised and when the tank becomes full, the water from the neutralisation tank is pumped todelay pond. If necessary, the acidic and alkaline effluent can be pumped separately to chromatetreatment plant.

5.1.5 API Oil FiltersIn each compressor house an API oil filter with coke packing is to be provided to remove oil

from condensate and clear water taken to storm water drains.

5.1.6 Steam Utility Plant EffluentsThe B F W purge water from boilers is to be separately taken in a header to a pumping pit

and from there, it is to be sent to delay pond for slow discharge.

5.1.7 Sewage Treatment By Anaerobic FermentationSewage is usually having high B.O.D value. The sludge is treated in sludge digestor under

anaerobic condition with agitation when soluble sludge collects at the bottom and removed. CH4 andCO2 gases are removed from top. Time for digestion is 12–50 days. The supernatant liquid fromdigestor is removed from top. There are 9 species of methane bacteria having different substrateswhich can be judiciously used for biological effluent treatment. In sludge digestion, percentage oftotal solids, conductivity, volume of sludge, pH and BOD value are indicators for efficient digestion.The digested sludge is then subjected to elutriation.

The fresh sludge suitable for disgestion may contain other alcohol soluble substances, cellulose,hemi-cellulose, lignin crude protein and ash (24%).

6. PRESSUREISED AIR FLOATATION PROCESS FOR OTHER INDUSTRIALWASTE WATER TREATMENT FOR

(i) Removal of pulp and paper fibres from waste water(ii ) Removal of oil from refinery waste.

(iii ) Primary clarification of sewage and thickening of sewage sludge.(iv) Full recovery of coal washery wastes.(v) Removing oils from metal processing wastes

(vi) Removing fatty acids and soaps from wastes water from soap works and processing ofedible oils.

(vii ) Removing suspended solids from cannery wastes(viii ) Clarification of laundry wastes(ix) Removal of grease and suspended solids from meat packaging units.(x) Waste water treatment from engine cleaning and paint stripping; etc.

The process consists of dissolving the gases in effluent liquid under high pressure and releasingthe pressure of liquid suddenly in a separator by taking out the effluent fluid by a horizontal dischargepump at 25-60 psig pressure. Alkali (for pH control) and coagulant is added to mixing tank as well

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ENVIRONMENT AND POLLUTION AIR AND WATER 267

as to pump discharge. Compressed air is added to pump suction and released from separator topand separator outlet fluid and is slowly fed to the conical floatation unit by a back pressure controlvalve. The bottom scrapper of floatation unit removes sludge and scum is removed from top offlotation unit and clear treated water over flows from top. About 5–8% free air dissolves.

The process is based on the principle of Henry’s law which states that increase of solubilityof gases dissolved in water varies with the absolute pressure of gas.

6.1 Food industry Waste WaterUltrafiltration by membrane method is used to retain organic substances in food industry’s

waste water. Pressure required is 10–20 m water column and dissolved materials pass through themembrane.

BOD Value % retention by membrane

(mg/lit)

18250 99.7

(Carbohydrates)

Potato starch 12700 85.1

Veg. Proteins 21500 99.6

Cheese whey 45000 99.3

Table 1Atmospheric Temperature above sealevel.

Height, KM NAME Temp°C

250 Thermopause 1027

230 Satellite Level

210 Thermosphere 27

70 Mesosphere – 3

30 Stratosphere – 73

10 Troposphere

Sea Level 7

Table 2

1. Limits of Pollutants as per Minas/IS 2490/Assam Pollution Board (For Namrup–III) for Final Discharge Effluents to River

Sl. Constituents Minas IS2490–74 Assam Pollution BoardNo.

1. pH 6.5 – 8.0 5.5 – 9.0 5.5 to 8.0

2. Temperature – < 40°C Shall not exceed 40°C

3. Ammonical Nitrogen. 50 mg/lit 50 mg/lit –

4. Total Kjeldahl Nitrogen 100 – 50

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268 REFERENCE BOOK ON CHEMICAL ENGINEERING

5. Free Ammonical Nitrogen 4 4.12 4.12

6. Nitrate Nitrogen. 10 – 20 (Nitrite and

7. Nitrite Nitrogen. – – Nitrate.)

8. Cyanide as CN 0.2 0.2 0.2

9. Venadium as V 0.2 – –

10. Arsenic as As 0.2 0.2 0.2

11. Flouride as F 10 2.0 –

12. Hexavalent chromium as Cr+6 0.1 0.1 0.2

13. Total chromium 2 – 2

14. BOD (5 days at 20°C) – 30 20

15. COD – 250 250

16. Oil and grease – 10 10

17. Total suspended solids – 100 30

18. Sulphate as SO4 – – 100

19. Chloride as Cl. – – 600

20. Dissolved oxygen. – – 3

21. Resedual chlorine – 1.0 1

22. Phenolic compound – 1.0 1

23. Total Dissolved solids – – 2100

24. Sulphides (as S) – 2.0 2.0

Table 3

2. Ambient Air Quality Standard as per Air Act. 1981

Area Category SPM SO2 CO NOX Remarks

Unit = µg/M3

A. Industrial and Mixed use 500 120 5000 120

B. Residential and Rural 200 80 2000 50

C. Sensitive 100 30 1000 30

AIR POLLUTION ABATEMENT

1. Electrostatic Precipitator

When dust/microbial cells pass through an electrified field (D.C), they become ionised with +vecharge and are collected on a negatively charged plate. The ionising wires are held at 13000 – 14000volts and the dust collecting plates are kept at 6000 – 7000 volts. The dust removal efficiency isabout 90%. The controlling factors are air flow rate, plate loading, electrostatic field intensity, sizeof dust and its dielectric properties.

Larger foreign particles and increased air humidity can cause severe damage due to sparking.A medium efficiency dust filtration system should precede the electrostatic precipitator and if required

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ENVIRONMENT AND POLLUTION AIR AND WATER 269

flue gases should be dehumidified. It is mandatory to use E. S. P for large coal based thermal powerplant.

2. Greenhouse Gases Fixation in Air

Reaction : CO2 + H2O + Sunlight chlorophyll → 2 2

carbohydrate

(CH O) + O

For each gm mole of carbon fixed, 470 kj (112 kcal) of energy is absorbed in the biomass.

Dissolved organic substances are usually susceptible to Biological degradation where as refractivesubstances are not accessible to microbial attack and are characterised by high C O D and contentsof organic carbon.

This is usually treated for removal by combined adsorption or flocculation and activatedcharcoal process. Activated charcoal has surface area of 600–1200 m2/gm and when used forremoval of organic matters most of the materials are removed. The active carbon mass is regeneratedby heat at 750–950°C.

6.2 Cement Industry Inorganic Waste MaterialCement dust from clinker kiln and cement grinding are usually removed by electrostatic

precipitators. In case of waste water from the dust scrubbing unit the waste water is taken to largelagoons for seepage and sedimentation and clear water is discharged from top of lagoons.

6.3 Porcelain Industry Waste(1) Preliminary screening, done to remove large coarse or broken particles.

(2) Combined chemical–mechanical methods for clarification.

Wastewater

Flo

ccul

atin

gag

ents

C larifier

Pump

Filter press

Treated efflu

ent

Fig. 1 A Porcelain Industry Waste Treatment.

The process consists of addition of flocculating agents (Al. Sulphate, lime or iron salts) in anadditional tank and holding waste for 5–10 mins and then taking into a clarifier or sedimentation tank.The sediments from bottom of tank is pumped to a filter press. The suspended matter is thusremoved and clear water after filter press. is discharged. (See Fig. 1)

6.4 Waste Water from Iron and Steel WorksThe recirculation water from Blast furnace wet gas treatment, cleaning towers and other

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270 REFERENCE BOOK ON CHEMICAL ENGINEERING

operations like flue gas purge water consists of aeration upstream of sedimentation tanks to blowout carbonic acid followed by sedimentation in tanks. The waste water consists of cyanogen,sulphur, phenol, ashes, iron oxide, silicic acid slag. Ore particles as well as Al, Carbon, Calcium, Mgand Zn compounds. By aeration, Calcium/Zinc hydrogen carbonates are converted to carbonates andprecipitated out with addition of flocculating agents–iron or Al salts as well as auxiliary flocculatingagent viz an organic polymer.

The sludges which collect at the bottom of sedimentation tanks, are recovered continuously andused for land fills.

Toxic materials like alkali cyanides are formed in B.F. gas and flue gases contain HCN ordicynide. The process of removal of these materials consists addition of formaldehyde to recirculatedwater to raise pH to 8–10 and keeping in delay pond for long hold up to convert the cyanides toharmless polymers.

6.5 Ttreatment of Waste Water from Picking PlantsFor treatment of waste water from metal pickling plants, usually one method is for recovery

of Fe+2 or Fe (SO4) 5H2O when HCL or H2SO4 is used for pickling and the 2nd method is byneutralisation with alkalies when acid pickling is done. Lime is used as a neutralising agent.

6.6 Waste Water from Electroplating IndustriesThe waste consists of mainly cyanides occurring as alkali cyanides (very poisonous) or as

complex cyanides. The process consists of, reaction with Sodium hypochlorite NaOCl (den.1.21 kg/lit and contains 12.5% active chlorine, corresponding to approximetely 150 gm of active chlorine (perlit) when cyanide is oxidised to chlorine cyanide which is then converted to cyanate at pH at about9.5 using NaOH. Both the temperature is kept below 38°C. The reactions are exothermic:

2CN− + 2OCL− + 2H2O → 2CNCL + 4OH–

2CNCL + 40H− → 2CNO− + 2C1− + 2H2O

2CN− + 2OCL− → 2CNO− + 2Cl−

Excess Hypochlorite @ 1% is used and residence time in reaction bath is about 20 mins. Airabove bath is exhausted by an exhauster which push the reaction vapours through a water scrubber.

Iron (Fe+2) salts can also be used to form complex salts ferricyanides Fe2 (Fe(CN)6.

6.7 Soda Ash Plant Waste WaterIt contains CaCl2 and sludge, containing suspended matters which are treated in a sedimentation

tank for 8–9 hrs when conc. of chlorides are reduced.

6. 8 Waste Water from Pharma IndustriesHere various methods viz detoxification, deoiling, neutralisation, treatment with precipitating

agents, decolorisation, sedimentation, biological treatment etc, are used and exact nature of treatmentwill depend on specific requirement. When separate treatment methods are to be used for each wastewater from a particular type of product, exact waste water treatment method is to be used.

6.9 Waste Water from Inorganic Dye and Colourant Plants’ IntermediatesThe waste water usually contains lead or arsenic compounds which must be detoxified by

using (1) Sodium sulfide to precipitate arsenic sulfide or (2) using (Fe+3) in an alkali solution toprecipitate Ferrous arsenate or adsorptive co-precipitation (3). In case of lead waste water, uses

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ENVIRONMENT AND POLLUTION AIR AND WATER 271

Sodium Carbonate to precipitate lead carbonate (4) Similarly for barium containing waste water, useof Sod. Carbonate is to precipitate barium carbonate (5) For chromate containing waste water toreduce Cr+6 to Cr+3 using Sod. metabisulphite in acid pH and then converting Cr+6 to Cr+3 followedby neutralisation with lime. (6) For TiO2 containing waste water, treatment with hydrated ironsulphate is followed by crystallization and reduction to Fe2O3 and H2SO4. The dil. acidified effluentis then dumped into sea or sent to delay pond.

In all these processes water after detoxification is stored in delay ponds for sedimentation andslow discharge to surface water.

6.10 Organic Dye and Intermediate Industry(i) Removal of colours–various methods are used to remove colour viz chlorine, Ferrous

chloride, Sodium hydrogen sulphide. Azo dyes are cracked by reducing agent, land filtration andbiological purification.

The combined method of chemical precipitation with biological purification gives satisfactoryresults in some cases of water treatment.

(ii ) The waste water, which is more from these industries are first neutralised if necessary. Thesegregated streams of waste water are treated individually w.r.t. their composition, treatment methodrequired and specific type of waste water. The waste water containing toxic substances–cyanidecompounds, arsenic salts, free chlorine, flourine bromine etc are detoxicated by chemical precipitationmethod. Oils and fats if present are retained in separators. Waste water containing mainly organicsubstances are treated by extraction, concentration by evaporation and other methods.

Strong odours from waste water are removed by aeration with fixed or floating aerators intanks, columns etc, by the treatment with Cl2. For all types of waste water neutralisation can becarried out together with NaOH or lime in aflocculator with built in stirrer for 15–30 minutes beforecoarse sludge flakes are sedimented for sludge removal.

For removal of high B. O. D level in waste water the treatment is usually done in digestorsfollowed by degasifiers to remove CH4 and CO2 gases under 20" vacuum and then separation ofsludge by tickling filtration and finally in clarifiers.

Anaerobic digestion of pulp and paper industry waste is carried out at 0.1 lbBOD/ cft ofdigestor/day only if sulfides formed are not allowed to accumulate in the digestor.

6.11 Dairy Effluent TreatmentWaste water from Dairy is first removed of oil in a oil trap and sent to equalisation tank from

where it is sent to anaerobic tank for fermentation. After anaerobic treatment, the effluent is treatedin series in two aeration tanks fitted with air aerator and sent to secondary settling tank. By-passarrangement is provided for use in either of the aeration tanks. Settling tank clear effluent from topis pumped to sludge draining filter and water is recycled to Aeration tank I or aeration tank–II. Heavysludge is removed from the bottom of sec. settling tank for disposal.

6.12 Sugar Mill EffluentThe process is similar to above except that lime is added to equalisation tank and a bar screen

is provided before oil trap to remove bagasse fibres.

6.13 Waste Water Containing MercuryWaste water from caustic chlorine plant using Mercury cell and other processes contains small

quantities of Mercury. There are 3 processes for removal of mercury.

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(i) In chemical process, Mercury compounds are reduced with Hydrazine or by precipitatingMercury as sulphide with thiourea or Sodium sulphide followed by filtration.

½ O2 + H2O + 2Na2S + Hg air→ HgS + 2NaOH

(ii ) By reacting Mercury with chlorine and adsorption in an ion exchange resin

Hg + 2HCl → HgCl2 + 2H+

(iii ) By Liq–liq extraction when Mercury conc. is reduced to < 0.01 mg/lit.

7. ENVIRONMENT PROTECTION ACT (EPA) 19867.1 The prescribed standard for liquid effluents along with parameters for each category of industrial

plants and others are given in schedule–1 of the EPA 1986. Often these standards and parametersare based on capacity of the factory. In addition MINAS (Min. national standards) for wastewater is applicable for some industries including stack ht. Fertiliser plant treated effluent qualityis given in table – 2.

7.2 The emission standards are also included in the Ambient air quality standard as per Air Act 1981categorises 3 different areas (industrial and mixed use, residential and rural and sensitive) forSPM, SO2, CO, NOX as given in table 3. For big projects continuous monitoring of atmosphericair, over the factory and at some distance along prevalent wind direction. E I A/ E M P reportis necessary for approval of the project either from central pollution control board or statepollution control board depending on whether the industry is under central govt. or stateauthority control. There are 23 projects industries which are under central pollution controlboard schedule – I plus all projects with threshold criteria above those specified in schedule –II under control of state pollution control board.

The schedule – II of the Act gives a list of 46 projects/industries which require state environmentclearance.

In order to get environmental clearance for a big project, it requires submission of E I A(Environment Impact Assessment) report and E M P (Environment Management Plan) alongwith D P R to concerned clearing authority (central and state). Such EIA/EMP reports are tobe prepared by central pollution board approved consultant.

7.3 Treated liquid effluents standard parameters are specified by MINAS or state pollution controlboard limits. Often IS standard is also available. The concerned plant authority is required tomaintain these limits, especially SPCB limits. In table–2 these standards for fertilizer planteffluent discharge limits.

7.4 Delay ponds (1+1) – usually treated effluents from effluent treatment plants are stored in delayponds (1+1) having 2 months capacity each from where it is discharged at out fall point afterthe rate of effluent discharge is measured in a weir (vnotch or rectangular). Often dilution wateris to be added before discharge to bring the effluent conc. below state pollution board standardor MINAS.

7.5 Under CPCB notification number S.O 318 (E) dt 10.4.97, the project authority would allowpublic views against the proposed project by keeping all project information including pollutionlevels (water and air) in concerned district DM’s office or office of central SPCB in the statecapital. District S.D.O will fix hearing dates from public for any complaints which can belodged in S.D.O’s office.

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ENVIRONMENT AND POLLUTION AIR AND WATER 273

8. C.O.DIt is a measure of the components which can be oxidised in chemical reactions. Amount of

Sod. permanganate or Sodium dichromate (oxidants) consumption in reaction determines the valueof COD.

8.1 B.O.DIt is the amount of Oxygen necessary for bacteria to consume organic matter in water and is

determined by means of O2 depletation of a diluted aqueous sample containing microorganisms.Usually it is determined in 5 days duration at 20°C i.e. B.O.D5.

9. AIR POLLUTION CAUSESAir Pollution occurs due to dispersal of the pollutants into atmosphere. The pollutants emerge

from chimneys of various furnaces, using fossil fuels, solid or liquid, automobile exhausts, variouschemical processes. The pollution is also due to the dispersion of dust particles which come fromgrinding operations, chemical dusts emission, furnace fumes and fumes from solid wastes incineratorsetc. The emitted gases are of varied nature viz smoke particles, CO2, CO, SO2. NOx, HF, NH3 etc. Theso called green house gases viz CO2 etc are responsible for increase in atmospheric temperature whichis responsible for global warming and melting of polar ice caps resulting in rise in sea water levels.Increased industrial activities and fast increase in automobiles through out the world are responsiblefor increase in green house gases in atmosphere. The emission standard is given in Table 3.

10. ANTIPOLLUTION MEASURES TO REMOVE AIR POLLUTANTS, VARY ACCOR-DING TO THE SOURCES OF POLLUTANTS. SOME OF THESE AIR POLLUTIONABATEMENT EQUIPMENT ARE AS FOLLOWS.

(i) Gravity settling chambers

(ii ) Suction air filters

(iii ) Bag filters for dusts

(iv) Electrostatic precipitator for dust laden furnace gases.

(v) Dust cyclones

(vi) Gas scrubbers for removal of fine dusts and soluble gases.

(vii ) Pulse jet bag filters for dedusting.

(viii ) Venturi scrubbers.

(ix) Air filter houses with reverse cleaning for removal of fine particulate matter.

(x) Dust and fume extractor.

(xi) 4th hole dedusting system for electric arc furnaces.

(xii) Burning of inflammable gases in a flare stack.

(xiii ) Use of high rise chimneys for dispersal of residual fly ash in atmosphere from coalbased power plants/cement klin

(xiv) Extension of chimneys with increase in static head of I.D fans where ever feasible.

(xv) Better design of burners for reduction in smoke and NOX.

10.1 (i) Gravity Settling ChambersFor separation of dust particles having diameter lower than 43µ , gravity settling chamber is

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suitable which is used for flow of dust laden air/gases having low degree of turbulance. Rectangularlong chambers are suitable for settling of heavier dust/soots. These gravity filters are rarely used nowand are replaced by more efficient filters.

(ii ) Suction Air FiltersThese are used for separation of dust of size 1–10µ from atmospheric air and are placed at

suction of air blowers, boosters or compressors. Atmospheric dust conc. depends of locality, itsindustrial units, wind velocity etc. In rural areas dust conc. is the lowest 0.3–0.5 grain/1000 cft, inindustrial area it is about 0.9–1.6 grain and in metro cities it is 0.6–1 grain. Life of air filters is short,usually 1–3 months.

There are 3 types of air filters, dry, viscous and continuous. Filtering media, is cotton, felt pad,glass wool, cellulose pulp wire mesh, corrugated fibre board, and cotton/syn. fibre wool etc. Inviscous type filters are coated with mineral oil (having high viscosity and flash pt.) Viscous filtersare having less thickness of filtering medium. Pr. drop across the air filter increases as more dustsseparate out. Maximum allowable pressure drop varies from 0.2 – 0.5 inch water. Dust conc. in anair filter is normally allowed upto 0.6 – 4 lbs for a 20" × 20" filter. Efficiency of dust collectionis usually 60–85%.

Automatic filters have continuous rotating moving perforated crimped or woven metalic screens.The washing arrangement is by water spray which is often of viscous type.

(iii ) Bag FiltersThese are having filtering media of woven cloth for fine dust laden air or gas mixtures which

are allowed to flow through the bags when dust particles separate and form a layer, inside the wallof the bags which increases the collection efficiency. Once the dust layer is formed, continuousseparation of dust takes place. Excess dusts from the layer fall at the bottom of bags and are takenout through seal lock. The filtered air/gas goes out of the bags. Automatic arrangement for shakingof bag filters at regular intervals is done when separated dust falls at the bottom and removed. Thisreduces the Pr. drop. A battery of woven bags are placed vertically with hopper and seal lockprovided at the bottom for collection of dusts. Dust particles size to be separated, varies. Thecollection efficiency could be 80–90%. Woven cloth has openings larger than dust particle dia. Thesefilters can have arrangement for automatic shaking for cleaning dust layer from inside the bags.

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VEGETABLE OIL REFINING

Chapter

47

1. THERE ARE VARIOUS TYPES OF VEGETABLE OILS VIZCoconut oil

Rape seed oil

Groundnut oil

Cotton seed oil

Sunflower oil

Soyabean oil

Rice bran oil

Corn oil

Castor oil

Lin-seed oil etc.

Out of the above oils, crude vegetable oils extracted from oil seeds except Rice bran oil whichis made from bran of paddy while rice dehulling process is carried out – the bran is the outer browncoating on rice and husk forms the outside hull of rice. Rice bran oil is made from rice bran by nhexane solvent extraction process. The crude veg. oils from corresponding seeds are usually expelledby mechanical expellers followed by refining by degumming process, alkali neutralisation process,bleaching process and deodourisation process. When mech. expeller is not used, rice bran is pelletisedand then solvent extraction is done in a series of 4 solvent extractors which also removes oil frommeals from oil seeds. Vegetable oils can also be extracted by suitable solvent extraction process afterthe cooked seeds are flaked in a flaking machine.

2. CRUDE OIL EXTRACTION FROM OIL SEEDS(i) Oil seeds, as it is received in oil plants, contain naturally occurring seeds, pods, earth and

often metal iron parts. Before storage, the foreign materials are removed by screening and aspirationand iron removed by electromagnet and sample is analysed for moisture content, oil content etc. Thefreshly harvested oil seeds contain as much as 20% moisture and grain must be dried to around 13%moisture for extended storage. High moisture reduces oil content, decrease in protein, increase incolour of extracted oil, and refining losses.

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Oil seed grains, if left unattended and temperature of storage is not checked, grain temperaturewill rise spontaneously and damage the seed for which it is to be either processed immediately orheap is shifted to another location.

(ii ) Drying of oil seeds, containing 20–50% oil, is usually done in direct gas fired furnace andhot gases move upwards and make contact with falling seeds from vertical drying tower. Other heatsource is, indirect steam heating of air in a heater or solar drying units. The drying temperature limitis 63°C; higher temperature will increase colour of meal and oil, denature the protein and will increasethe phosphatide levels in crude oil and even grain fire may occur. Storage should be of concretestructure.

(iii ) Oil expelling by mechanical expellers: The oil in seeds are lightly bound with the cell andmechanical pressure is applied to remove the oil by expellers which are located in the seeds preparationsection building. The operation involve cooking, pressing of dried seeds, cake cooling, finishing andcrude oil filtration.

Oil seed or seed flakes (whenever required) are put into vertical stacked agitated cooker whenheat is applied. After cooker, hot meals enter screw presses or multiroller expellers. Modern batchprocess uses hydraulic presses at 300 – 500 kg/cm2 press.

In open type haudraulic presses, seeds must be wrapped in pressure standing cloth and theclosed type are provided with pots and cages. In screw presses the applied pressure is very high(upto 3000 bar) and process is efficient as oil upto 98% can be expelled. Usually oil removed variesfrom 60–98%. The oil cake passes through end plate and becomes hard and oil comes out throughdrainage bars. After the cake is broken and cooled it is sent to solvent recovery section, if installedfor further recovery of oil. In case solvent recovery of oil from cake is not desired, the expellersare operated with the highest pressure. The crude oil, after expellers, contain fine meals which isremoved in scheming tank followed by filtration in press leaf or plate and frame filter presses.Crushed vegetable oil is sent to storage or sent for refining. The quality of oil is higher than solventextracted one because less oil soluble impurities (viz phosphatide etc) are removed. Removed finemeals are sent to pressure flaking operation for further recovery or sent for solvent extraction ifdesired. Oil seeds are often subjected to flaking operation by a flaking roller if needed for better oilextraction in expellers. Mechanical extraction is suitable when oil seeds contain over 20% oil.

3. RICE BRAN OILIt is a desirable vegetable oil and which is harmless. It is produced from rice bran by n–hexane

solvent extraction. Better solvent is isopropyl alcohol due to its low inflammability. By solventextraction very low residual fat content can be achieved. (Apart from rice bran, whenever otherseeds are used for solvent extractions, where oil content is less than 20%, Iso-propyl Alcohol whichis a better solvent due to its low inflammability and having B.P. of 55–70°C which can be steamstripped-can be used.) Hexane can be removed from oil at temperature below 100°C in vacuum. Thesolubility of water in hexane is only 0.1%. The process of crude rice bran oil production by solventis given in Fig. 2. The solvent dissolves only glycerides but not undesireable materials viz colouringmatter, gums or phosphatides. Since rice bran contains 8–16% vegetable oil, it is usually processedby solvent extraction after drying of brans followed by pelletising.

Solvent extraction of seed flakes or rice bran consists of cylindrical vessels of size with highD/H ratio and fitted with a sweep agitator with scrapper to remove the extracted seed flakes or branduring solvent stripping with steam (direct and indirect steam heating) solvent inlet/outlet facilitiesfor pumping and crude oil inlet. A 3–5 m3/hr capacity extractor with 5 such batch extractors in series

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VEGETABLE OIL REFINING 277

is capable of producing 600 MT/day rice bran or other veg oils. Hexane required is 50 MT. Often4 stage solvent extraction of pelletised rice bran or meals from oil expellers after filter pressing isused. Solvent extractor using 4 stage extractors where meal, rice bran pellets/seed flakes and solventfrom previous extractor is used and fresh solvent enters into 1st extractor and successively moveto last or 4th extractor. Flow sheet using one extractor is given in Fig. 1.

Fig. 1 Block Diagram for Solvent Extraction Process for Oil Seeds

Flow in extractor is counter current where pure solvent comes in contact with, meal/flakes andpellets which already have been largely extracted or vice versa, in both batch and counter currentprocess. The solvent rich oil is then steam stripped in a steam stripper to remove solvent and recovervegetable oil. The solvent is then rectified in a distillation tower in vacuum to remove dissolved oil. Thesolid meal from extractor is further treated with hexane to remove residual oil in meal (cake), driedand cooled and then sizing operation with grinding is done. The fixed meal is then sent to storage. Thecrude rice bran oil is then either subjected to miscella refining or further subjected to refining processwhich gives a light yellow colour to rice bran oil and is a relatively stable edible oil. Rice bran oil hardensat 30–35°C and is often used in margarine. The properties of vegetable oils are given in Table 156/158in vol. IIA and its empirical formulae for physical properties in table 155 in vol. II.A.

4. REFINING OF CRUDE VEGETABLE OILSThe crude vegetable oils contain phosphatides, carbohydrates, protein, fatty acids and toxic

compounds (Pesticides etc.) Therefore, refining operation, are carried out to remove these materialsas far as possible without affecting main constituents, vitamins and poly unsaturated fatty acids.

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However, some vegetable oils viz. castor oil, olive oil, linseed oil or cold pressed sunflower oilsare not refined in order to preserve the main properties of these oils. The refining operations aredescribed briefly as below.

(i) Degumming operation to remove phosphatides from vegetable oils, containing highphosphorous viz corn and sunflower oils, by water degumming to remove water hydrateablephosphatides only. For NHP removal, special treatment is necessary. Phosphatides, gums and othercolloidal compounds promote hydrolysis of an oil. In hydration, degumming oil is treated with wateror steam, to form a sludge that is insoluble in oil. This is used to remove lecithin (1–3%) fromsoyabeen oil containing 2.5% H2O by mixing with crude oil at 70–80°C with contact time 1–30mins. The sludge is separated by contrifugation with addition of citric or phosphoric acid aftermixing with crude oil which increase hydration. The process varies depending on crude oil. Preliminarycrude treatment with bleaching agent or other adsorbent, in presence of citric or Phosphoric acid,can be helpful. Some oils can be degummed by heating upto 240–280°C.

Refining by distillation is possible for low Phosphatide content. Special degumming techniqueinvolves the addition of citric acid, followed by hydration at 70°C for several hours beforecentrifugation. The flow sheet is given in Fig. 2.

(ii ) Neutralisation Process

Vegetable oils contain 1–3% FFA. It is removed by treatment with caustic lye or distillation,when soap solution is used. Other undesirable constituents viz oxidation products of fatty acids,residual phosphatides, gums, phenol and toxins are also washed out.

Fig. 2 Vegetable oil refining process including rice bran oil

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VEGETABLE OIL REFINING 279

(iia ) Alkali NeutralisationHere conc. lye of (4–7 N) with crude oil is used in a reactor fitted with steam heating coil and

live steam heating upto 40–80°C with strong lye which settles at the bottom. For weak lye, it issprayed to crude oil at 90°C to neutralise FFA. After neutralisation and discharge from reactor, crudeoil is washed with dil. lye (0.5N) and then with water to reduce residual soap to 500 ppm. conc.Incomplete removal of soap impairs colour of oil and efficiency of following refining steps. Soyabeenoil is subjected to post treatment with Na2CO3 and silicate to remove residual traces of oxidisedglycerides and phosphatides. Soap stock can be used in boiler fuel or it can be converted to acidoil, used as animal feed or other use. The quantity of acid oil (mix of fatty acid and neutral oil) isvariable.

(iii ) The method to remove FFA is by distillation or neutralisation in vacuum after degummingoperation. The process is suitable for rape seed, soyabeen and sunflower oils with the technologyavailable for reducing phosphatide content. Distillation temperature required is 240–270°C when FFAcontent become less than 0.1% .

Other process of esterification with a catalyst is also available.

A refining factor of 2 means that for each mass unit of free fatty acid (FFA) in crude oil, 2mass units of acid free oil is produced. Process flow sheet for alkali neutralisation is given in Fig. 2.

(iii ) Bleaching OperationDegumming and alkali neutralisation do not generally give significant decolourisation. The

process involves the use of Fuller's earth (bleaching earth) and/or activated carbon (charcoal) fordicolourisation of crude oil. The process of neutralisation and bleaching is usually carried out togetherin a vessel fitted with agitator and vessels connected to vacuum. The crude oil is mixed with Fuller'searth, stirred and filtered off. The bleaching should be done below 100°C through steam coil inbleacher. Oil retention in bleach is 50% of bleacher or 100%(wt) of activated charcoal when usedin combination with F.R. (Fullers earth).

The operation is carried out under vacuum as bleach catalyzes the oxidation of oil. Process iscarried out in air free atmosphere including filtration, after discharge from bleacher. Some timesbleaching is carried out at 65°C and 100°C and preceded by addition of citric acid and Phosphoricacid to chealate trace materials and to precipitate hydrated phosphatides. Soap solution and washwater are introduced from bottom nozzle. Pigments to be removed are condenoids and chlorophyl;but the bleaching operation also reduces phosphatides, soaps, trace metals and oxidation productssuch is H2O2 and non volatile polar decomposition products.

Bleaching earth (mainly Al silicate) containing 5–10% moisture is first activated and dried.Quantity of activated F.R will be 0.5–1% and activated charcoal (0.1–0.4%) is used when there aredifficulties in bleaching. The crude oil is dried in vacuum for 30 mins at 30 kpa and adsorbent earthis added and stirred for about 1–30 minutes in vacuum at temperature of 80–90°C. The slurry ispumped out to special filter presses or closed disc type centrifuge which have limited air access.Bleaching and centrifugation is done batchwise. The colour in crude oil is mostly removed. Theprocess is given in flow sheet in Fig. 2.

(iv ) Deodourisation ProcessHere odours/flavours in crude oil are removed from bleached oil. The process uses steam

distillation under vacuum, when volatile compounds (odour and flavouring agents) are removed fromnonvolatile glycerides. The odour causing compounds in crude oil are primarily aldehydes and

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ketones formed by auto oxidation during handling and storage and usually has threshold value of afew ppm. Other volatile compounds (FFA, sterols or phenols) are also partially removed. Theflavouring compounds can also be formed by hydrolysis and thermal decomposition of crude oil.Distillation under vacuum is necessary due to low partial pressure of removeable compounds. Steamconsumption rate is 5–10% wt. of crude oil for batch process and 1–5% wt. for continuous process.Distillation temp. is 190–270°C at press. 0.13 to 0.78 Kpa (1–6 mm Hg). Steam required is 10–20m3/kg of oil. The distillate removed is about 0.2% of oil and contains very little oil. Time required forbatch process is 4 hrs. The end point is determined organometrically. Steam used must be free fromoxygen and dry. To deactivate peroxide. Like trace metals, aq. citric acid soln. (2–5 mg c. acid/100gm of oil) is often injected into the oil towards the end of decomposition. The sketch of batchdeodouriser is given in Fig. 2.

5. HYDROGENATION OF VEGETABLE OILSThe double bonds in fatty acid chain can be mostly or partially saturated by adding Hydrogen

in presence of nickel, platinum or palladium catalysts which increases the m.p and make thevegetable oil solid at room temp.

6. PROPERTIESNaturally occuring vegetable oils are liquid or semi solids consisting of glycerides. Liquid oils

are termed as liquids vegetable oils and solids as fats. Such oils also contain minor constituents offree fatty acids, phospho liquids, sterols, hydrocarbons, pigments, waxes and vitamins. The veg. oilsusually contain 97% glycerides i.e. triesters of glycerol with fatty acids, upto 3% diglycerides andupto 1% monoglycerides. They constitute 3,2 and 1 molecule of fatty acids respectively and triglyceridescontain at least 2 different fatty acids groups. Their physical, chemical, and biological properties aredetermined by type of fatty acids group present and their distribution over triglycerides molecules.M.P of oils increases with the increase in long chain saturated fatty acids or decreasing proportionof unsaturated or short chain fatty acids.

Fatty acids are generally even numbered, straight chain aliphatic monocarboxylic acids withchain length ranging from C4–C2. The no. and position of double bonds in unsaturated fatty acidsdiffer in configuration (i.e. cis or trans isomers)

The common fatty acids are butyric, lauric, palmitic, olive, stearic and linoleic, acid. Crudefatty acids contain significant quantity of free fatty acids, FFA and most vegetable oils containpalmitic, linoleic and olive oils.

Glycerides can be hydrolysed, as seen from refining processes, into fatty acids and glycerols.

CH OCOR CH OH

CHOCOR H O CHOH RCOOH

CH OCOR CH OH

2 2

|

|

2|

|

2 2

+ → +3 3

Unsaturated fatty acids in oils and fats can be polymerised by heating at 200–300°C formingdimeric, oligomeric and Polymeric compounds.

Auto oxidation of veg oils develops rancidity, off flavour and reversal of flavours duringproduction and storage. Oil cake and spent bleaching earth (Fullers earth) can cause sponteneouscombustion.

High moisture content in oil seeds help uptake of oxygen resulting in degradation.

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VEGETABLE OIL REFINING 281

Rice Bran Oil

Saturated fatty AcidsC4 constituent = 0.58 gm/100gm fatty acids

C16 constituent = 13–18 gm/100gm fatty acids

C18 constituent = ~2 gm/100gm fatty acids

C20 constituent = ~0.5–1 fatty acids

C24 constituent = 0.5 fatty acids

Unsaturated fatty acidsC18 : 1 = ~44 gm/100gm fatty acids

C18 : 2 = 30–40 gm/100gm fatty acids

Density of R.B oil vary from 0.916 – 0.921 gm/ccSap value = 183–194 (mg KOH)

Iodine value = 92–109

N S M = 3.5 – 5.0 gm per 100 gm oil

MP = ~10°C

R. I (nD40) = 1.466 – 1.469

R. B oil is most suitable edible oil as its saturated fatty acid content is the minimum or so.

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FURFURAL

Chapter

481. FURFURAL, C5H4O2, MOLECULAR WT 96.08 IS AN INDUSTRIALLY IMPORTANT

CHEMICAL AND A STARTING MATERIAL FOR FURANS.

1.1 PropertiesIt has excellent thermal stability in absence of oxygen upto 230°C and exposure for considerable

hrs is required to produce detectable changes in its physical properties with the exception of colour.A fresh distilled furfural is a colourless liquid with a obnoxous aromatic smell similar to almonds.It darkens in air due to presence of oxygen.

Furfural is an excellent solvent with low viscosity over a wide temperature range. It mixes witha no. of organic solvents but is slightly miscible with saturated hydrocarbons which makes it aselective solvent for a no. of industrial uses viz. in petroleum refinery. Chemical properties of furfuralis similar to aromatic aldehyde (Benzaldehyde) with other reactions due to dienic character of furanring. The vapour pressure of furfural is given below.

Temp °C 55 75 95 105 130 150

V.P, KPa 1.97 4.60 11.18 19.7 39.5 78.5

Furfural is reduced to furfuryl alcohol and can be oxidised to furoic acid and decarbonated tofuran, catalytic vapour phase oxidation of furfural yields malteic acid.

Flammability of furfural is similar to that of hexane or no. 1 fuel oil. It should not be mixedwith strong alkali or acid and stored near strong oxidising agents. Usually a few pentosan containingmaterials (Xylan) are used to manufacture furfural.

1.2 Manufacturing ProcessRaw materials – Rice husks, hulls of cotton seed husks, oats hulls and cereal grains. Other raw

materials are, wheat chaff, bagasee, corn cobs and deciduous and coniferous tree woods, sulfitewaste liquor and cellulose waste liquor.

Meterial % pentosan content Avg. Furfural Content,%

Cotton seed husks 23–28 18.6

Bagasse 25–27 17.4

Corn cobs 30–32 23.4

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FURFURAL 283

Material % Pentosan content Avg. furfural Content, %

Oat husks 40 22.3

Corn stalks 24 –

Birch wood 25 –(after tannin extraction)

Corn husks 30–33 –

Wheat chaffs 18 –

Pentosan is the main constituent in Xylan–a polysaccharide with β–1, 4– linked D–xylopyransoneunits together with small amount of arabiran, a highly branched polysaccharide of 1,3 and 1,5 linkedα–D cerbinofurarone units. Xylan in cereal strawps and grains constitute 23–30% and about 15–25%in deciduous tree wood and 5–15% in coniferous wood based on dry matter.

Process – The raw material, such as bagasse, is charged in a batch or continuous digestor withaddition of a strong mineral acid and H.P. steam is passed to raise temp of digestor. After operation,temp. and press. of digestor is attained and the spent reaction material is withdrawn from digestorand furfural water vapour from the top of the digestor is condensed in a condenser with coolingwater.

The condensed digestor vapour, containing furfural-water mixture is stripped with H.P. steamstripper and the vapour from top of the stripper is condensed in a cooler and put in a decanter wherefurfural containing 6% water, settles at bottom as being heavier than water and water forms the toplayer in decanter.

Liquid furfural is pumped to dehydrator (Rectification Column) to obtain pure furfural (98%min.) which is tapped out from the bottom of dehydrator while top vapour of moisture with 8%furfural, is condensed in a condenser and drained to decanter for recycle. Water from the top ofthe decanter is periodically drained.

The cellulosic material in digestor undergoes partial degradation during digestion and remainswith lignin and ash in the residue, this is burnt in steam plant as a fuel support for the energy requiredfor furfural plant.

Reaction in digester:

Another form of reaction:

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1.3 Handling, storage and Transportation of furfural in steel tanks, All steel tank trucks and steeldrums are used. Proper packing in valves should be used to make them leak proof becausefurfural is an excellent solvent. The storage tanks/drums should be oxygen free. Colour changeof furfural is associated with acidity increase and polymer formation occurs when furfural isstored for long time in presence of air

1.4 Uses(i) Extractive distillation of C4 and C5 hydrocarbons for the production of synthetic rubber.

The use has come down due to butadiene availability from ethylene.

(ii ) Furfural is selective solvent for separating saturated from unsaturated compounds in Petrolubricating oils, gas oil and diesel oil.

(iii ) It is a solvent for furfural alcohol resin for fibre glass reinforced plastic articles.

(iv) As a flame retardant in plastic articles.

(v) Extractive recovery of butadiene from cracked refinery gas.

(vi) As insecticide, herbicide, fungicide and enbalming fluid.

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POLYETHYLENE TEREPHTHALATERESIN (BOTTLE GRADE)

Chapter

49

MANUFACTURING PROCESS1. It is manufactured by reacting Monoethylene Glycol (MEG) with pure terephthalic acid (PTA)

in presence of additives, comonomer–Isophthalic acid (IPA) and Diethylene Glycol (DEG) whenbottle grade PET (Food grade) is desired to reduced MP of PET and increase the crystallisationpoint. A catalyst, Antimony based, is also required to enhance reaction rate.

The German process (Zimmer) consists of initially making the oligomer formed by solid statepoly condensation and finally is subjected to solid state polymerisation.

PTA + 2 MEG →Oligomer + 2H2O ... (1)n(Oligomer) → (n–1) MEG + PET ... (2)

2. PROCESS DESCRIPTIONThe Polycondensation process involve first formation of oligomer from a thick paste in a paste

preparation vessel where MEG (liquid) and PTA (Powder) are mixed intimately. This thick paste isesterified in a series of two esterification reactors having internal heating coils using heat transfermedia (Therminol 66 liquid) circulation. Therminol vapour is used in jackets of esterification reactors.Liquid therminol temperature is around 325°C. The MEG V.P. in the EST reactors – I and II isincreased above atmospheric by heating of reactants so that reaction rate increases. Esterification iscompleted by transfering reactants and reaction products in 2nd esterification reactor, EST–II througha transfer pump. The reaction liberates water as per reaction (1).

The vapour from esterification reactors, EST–1 and EST–2 contain water and MEG is condensedand sent to a distillation column where the effluent water is distilled and taken out as distillate andsent to effluent treatment plant for reduction of BOD, COD and neutralisation. MEG accumulatesas a bottom product of distillation tower as its B.P. is 197.4°C. The quantity of distillate waterliberated gives the amount of conversion.

3. POLY CONDENSATIONThe reaction product is then transferred to pre–polycondensation reactor–1 (PP–1) by gravity

where vacuum is maintained by vacuum pumps and reaction temperature, at higher desired level, byheating coil using HTM fluid (Therminol 66). Poly condensation reaction starts in PP–1 and finalPoly condensation reaction is completed in PP–2. The reaction product is transferred from PP–1 to

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PP–2 by gravity. In PP–2, having similar HTM heating coil, the product temperature is furtherincreased. The vacuum level is miantained here as in PP–1.

The product from PP–2 is transferred to a disc ring reactor (DRR) with the help of a Polymertransfer pump. vacuum level in DRR is more. The vacuum in PP–II and DRR is maintained by MEGvapour jets and vacuum pumps instead of steam.

The vapour from waste water distillation column vent and vacuum pumps discharges are sentto a scrubber where any residual organic material is scrubbed and waste liquor is sent to the effluenttreatment plant.

In PP–II and DRR, the MEG liberation occurs as per reaction (2) and is enhanced by Polymerfilm formation due to agitation of contents in these vessels. The MEG vapour liberated is condensedin the scrapper condenser of each Polycondensation loops and recycled to paste EST–I and IIreactors.

A gear pump transfers the viscous product of DRR via 3 nos product filters. The filtered PETPolymer is then fed to 3 nos cutters (under water strand granulator) where the polymer getsquenched with DM water and granulated into chips. The chips are then transferred by conveyorsinto intermediate product silo storage.

4. SOLID STATE POLYMERISATION

The amorphous PET resin thus obtained is upgraded (bottle grade) to get an IV (intrinsicviscosity) lift to final level by solid state polymerisation.

The amorphous PET chips from storage are then conveyed into a dosing vessel. From dosingvessel the chips flow by gravity via a rotary lock into the precrystallizers where the chips arefluidised by hot pure Nitrogen gas thus increasing the chips temperature. The residence time inprecrystallizer is such so as to initiate crystallization of chips. Temperature of N2 and flow of chipsis controlled, otherwise the chips will stick to the precrystallizer inlet. The circulating N2 gas isheated up in a finned H.E. with hot liquid HTM flowing through the finned tubes. The heat ofcrystallization is highly exothermic.

The precrystallizer product chips flow by gravity into the rotary crystallizer which is having2 nos paddles rotating in opposite direction with liq. HTM, flowing through the paddles from inside.The crystallizer bottom having slope towards outlet and crystallizer jacket heating by liq. HTM.Further crystallization of chips occurs in rotary crystallizer due to increased heating of the jacket andpaddles heated by liq. HTM. A stream of hot nitrogen gas is passed through the crystallizer to removechip dust, produced by rotating paddles.

The crystallised chips are then conveyed by hot nitrogen gas into the solid state reactor (SSP)when IV of the chips are raised to the required value for bottle grade PET. The rise of IV (Intrinsicviscosity) depends on

(i) IV of base chips and its size(ii ) Carboxylic end groups

(iii ) Catalyst concentration used in Poly condensation(iv) Residence time in SSP reactor and(v) Dew point of circulating hot gaseous nitrogen gas.

The hot N2 gas enters into the conical bottom of SSP reactor while the chips are fed from apoint above this section which keeps the chips agitated and lifts the IV of the chips while hot N2

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gas becomes impure. The impure N2 gas is treated in Nitrogen processing unit where oxidation bycompressed air is carried out in O2 reactor in presence of Platinum catalyst. All hydrocarbons presentin impure nitrogen are burnt in presence oxygen and temp. of reactor is maintained high. The pureN2 thus obtained is taken out of oxygen reactor and is dried in a molecular sieve drier for moistureremoval. O2 content in N2 gas outlet of the reactor is monitored by an oxygen analyser (cartherometer).The chips from SSP reactor with increased IV, are fed into deduster cooler by gravity through arotary lock and chips are cooled and dedusted by compressed air. The product PET chips are thenstored in storage silo where it is bagged in 25 kg bags or jumbo bags.

5. SPECIFICATION OF FINAL IV LIFTED PET CHIPS IS AS FOLLOWSIntrinsic Viscosity (IV) at 25°C, P+DCB, dl/gm – 0.72 to 0.86

D E G Content, wt% – 1.0 – 1.5

Carboxyl end group, µg/kg – 35 (max)

I P A content, wt% – 1.5 – 2.5

Chips wt, gm/100 gm chips – 1.7

Acid Aldehyde, ppm (wt) – Max 1

Antimony content, ppm (wt) – 170 – 250

6. RECYCLING OF PET BOTTLESNow-a-days,. IV lifted PET bottles can be recycled as per developed process of manufacture

by which clean PET bottles are cut into chips and using extrusion moulding process, new bottlescan be made. For less clean PET bottle, PET is subjected to degradation by glycolysis and othersteps for recovery.

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PROCESS EVALUATION OF ACHEMICAL PLANT

Chapter

50

1. Whenever a detail process engineering package has been supplied by a licensing organisation orplant designer concern, it is imperative to subject the design and process engineering documentsto close scrutiny for any shortfall or inconsistencies in the package offered.

The following preliminiary checks are to be made.

(i) Whether the package given is in line with the requirement of the project for a new plantfacilities or for expansion of existing plant facilities or for debottlenecking additional facilities.

(ii ) The process informations or data supplied by the designer are to be tallied for the basicprocess engg. documents viz process flow diagram with material balance, piping and engg. flowdiagrams, equipment data sheets and major equipment drawings, instrument schedule etc. Theprocess designer is reqd. to supply their piping and material specifications to project authority oroperating co.

(iii ) To check the basic data, supplied by project authority on ambient conditions, wet bulbtemp., safe soil bearing load, wind, velocity with maxm. wind speed, water table and seismic dataand ISI seismic standard to be used, and electrical supply data etc. have been used by the designer.

(iv) Specification of equipment are to be checked for suitability.

(v) To prepare project cost estimate with cost data supplied or determined from other sources.

(vi) To determine project economics and financing mode and to determine viability.

2. Secondly, plant capacity rating is to be examined with the limiting equipment size/capacity withsimilar plants existing elsewhere with same or improved process with additions. Process materialbalance is to be checked for missing or inconsistent flows. The fuel, power, steam and processraw, material requirements are to be compared with available data for similar plants aboutadequacy and proper consumption norms. A detailed study is also to be made to narrow downthe gap between process Licensor's standard package supplied with the specific requirement ofthe project or operating co.

3. HEAT AND MATERIAL BALANCE CHECKSThe data furnished by licensor for these items are to be thoroughly checked for any deviation/

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missing items for any deviation/missing items in these vital process requirements. The licensor is tobe asked to give energy balance for different sections of plant and atmospheric emissions.

The operating company is to undertake EIA (environment impact assessment) study aroundplant by an authorised environment study agency as per requirement of local regulation for mediumand big process plant, taking into account the possible impact of effluents (air and water) releasesas per data supplied by process licensor.

4. UTILITY BALANCE(i) A study is to be made for peak and normal power requirement including emergency power

provision as per electrical balance given by the licensor. Even full or part power generation insidethe plant is envisaged, a comparative study on cost aspects is to be made for outside power vis-a-vis own generation. The emergency power installation should have appropriate fail safe auto start-up system. Receiving substation for outside power and control system should have high reliability.The licensor shall supply the electrical distribution arrangements to different plants, utilities, auxiliarybuildings and administration buildings. Substation with MCCs are to be clearly rated. Emergencypower supply need to be provided for plant lighting and critical equipment for safety during powerfailures. Due agreement with local electricity board or company is to be made once total powerrequirement is given by the licensor and when auxiliary power requirements have been finalised.

(ii ) Steam balance for the project or expansion as given by the licensor, is to be checked soas to ascertain the capacity of steam plant required, using a 25% excess capacity to cover for extraprocess consumption and leakages. The condensate is normally reused after cation polishing, followedby mixed bed treatment in ionexchange plant of the factory. Good quality steam traps for steampiping should be laid at 50 m distance with gradient of 1 in 200.

(iii ) Cooling water balance: Normally induced draft cooling tower is used and is sized adequatelyfor about 15–20% over capacity. The cold water temperature will depend on dew point and coolingrange. Dew point and relative humidity are also to be calculated theoritically when actual data arenot available from metrological department's long span data and psychrometric chart. Parabolicnatural draft cooling tower is often used when circulating volume is higher and cooling range is lowand wind velocity is less. Cooling approach is to be judicially selected. Wind velocity is to beconsidered for mechanical draft cooling tower as waste humid heat for cooling tower is to beadequately dispersed into atmosphere. Provision for emergency cooling water pump is to be madewith emergency power supply. The cooling water circuits, both incoming to outgoing from coolingtower, is to be checked for pressure drops so that the sum of the pressure drops is 0 as per Caseyformula. Dew point temp. can be found from steam table knowing the partial pressure of watervapour. Heat load in a cooling tower is expressed in kcal/hr or MW.

Cooling approach = Cold water temp – W.B. temp.

Cooling range = Hot water temp – Cold water temp.

W.B. depression = D.B temp – W.B. temp.

Relative humidity = Partial pressure of water vapour at any temp. pw

vapour pr. of water at existing temp. p w=

°

Renault’s equation : cs' – c = A.P (T – T')

for determination of wet bulb temp.

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Where, c = V. P. at temp (to be, determined)

cs' = Satd. V.P. at temperature T', mm Hg.

T = D.B. Temperature

T' = W.B. Temperature

A = Constant

P = Total atm. press. mm Hg

Absolute humidity (molal) =pw

p pw−

percentage molal humidity = 100pw p p°w

.p°w p pw

− × − where, pw = partial press. of water vap. at any temperature

p°w = vap. press. of water at existing temperature

p = Total atm. pressure.

Waste Water Generation and TreatmentThe licensor should indicate the qualities, temperature and pressures of waste water generated

per hour per day from each section of the process and utility plants. The analysis of waste waterfrom each section is important. The licensor is required to inform the statutory requirements ofeffluents to be discharged into natural streams, rivers or lakes after treatments for which the licensoris to give guarantees. It is advisable to have two impounding ponds of sufficient capacity for storageof effluents should the analysis of outlet stream/streams from effluent treatment plant goes beyondthe stipulated limits or break down of treatment plant. The acidic and alkaline effluents from D.Mplant need to be neutralised before discharge to effluent sewers. Inside plant sections separateeffluent sewers and rain water sewers are required to be put. Boiler blowdown should be collectedin pipe lines and discharged to effluent sewers as per statutory requirement and also for hazardouseffluents from plants and pump leakages. Cooling tower blowdown also needs treatment for chromiumremoval (hexavalent to trivalent).

Often effluent treatment plant is kept outside the perview of Licensor’s scope of work and thesame is designed by contracting firm as per specification of effluent given by licensor which ischeaper and the firm gives the guarantee for treated effluents.

(iv) Air PollutionThe licensor is to be given the statutory limits as per air pollution act for emission through

chimneys/stacks based on which the licensor designs the plant for proper atmospheric emissionmonitoring system which is required for large plants along with wind velocity indicator and directionof wind indicator. EIA report gives the velocity and direction of the wind and also indicates anyinversion level. Large coal based steam/power plants need electrostatic precipitator.

(v) Instrument air and auxiliary air servicesDried instrument air at 6–7 kg/cm of pressure and dew pt –40°C is normally required in a

process plant. The Licensor is to give proper scheme for I.A. system consisting of Air compressure(Reciprocating/centrifugal), silica gel driers (auto change over) with 1 + 1 heaters (steam and power)and a central dry air receiver to cater for atleast 20 mins after power failure. Individual plant sections

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also need to be provided with I.A. receivers of atleast 20 mins capacity for safe shutdown. Emergencypower is required to be provided for atleast one air compressor and heater for I.A system. Aircapacity should be made atleast 20% more than normal requirement due to leakages.

A small auxiliary air compressor is required to be put for service air requirement in plants andmech/elec/instrument work shops.

5. DESIGN CHECK POINTS(a) Material Balance

To indicate each item of flow with quantity, temperature and pressure at different points offlow sheet along with utility streams. Percentage conversion is to be ascertained from flow conditionsin the reactor or at converter inlet and outlet. Critical items are often shown in ppm and itsimportance in products, intermediates and raw materials are to be evaluated.

(b) Utility Balance

To check for compatibility with process flow diagram, steam production and fuel input, airflow etc. are to be ascertained to find out energy consumption, and excess air in steam generationand power plants. Instrument air, service air, nitrogen (for purging), C.W, C.W for pump glands areto be specified by licensor.

(c) Metrological data with 95% extreme temperuatre for 50 years average data, 100 years flooddata, seismic data as per IS code 1893 and earthquake factor/code are needed. Water table of thesite and source of factory water with analysis. Soil bearing load data are required and if not available,test bore is to be made to ascertain the soil bearing load and water table.

The data on the wind velocity and direction of wind for last ten years, with maximum windvelocity have also to be ascertained as these data are to be furnished to licensor prior to design ofthe plant. Analysis of fuel and its source and pressure/temperature etc., as well as raw materialsource with analysis are also to be furnished to process licensor.

(d) Auxiliary Services

Although these might not have been considered in agreement, it is important to have maintenance(mechanical, elecctric and instrumentation) requirements spelt out by licensor, along with analyticalrequirements and manuals, storages for raw materials and products, fire services and safetyrequirements for personal protection and gate office for punching and security.

Secondary systems – Start up requirements of spare equipment, refrigeration system in process,hydraulic systems of rotating equipment as per vendors etc., are to be clearly spelt by licensor orvendor drawings supplied to operating company.

(e) Plant Operating Safety

The licensor is required to provide flare system with tall stack, trip systems provided in processcontrol description reports, emergency stoppage of Hazardous storage systems in case of mechanicalfailure of storage vessels/outlet line.

Hazards of operation study in a process plant is helpful for better safety in operation.

Hazop–1 study is made before process design; Hazop–II analysis is done when process designis in advance stage and that for Hazop–III when the plant goes into commissioning.

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(f) OffsitesRequirements of loading and unloading of production and raw materials, plant roads, railway

siding (if required) are to be taken inoaccount. The factory act requirements of rest rooms andlavatory, lockers for factory staff, plant storages, process central control rooms, technical and admn.building, modern communication systems provision are required to be considered with some inputavailable from licensor like product bagging. and storage, railway siding etc. The hand railing andtoe foot board and equipment guarding requirements as per factory act are also to be considered.

(g) Land for Factory and TownshipLand requirement for factory is given by licensor in the plot plan which is to be checked. The

land includes areas, not shown for off sites, utility and auxiliary services. In addition, safe distancesfor Hazardous chemicals storage layout as per statutory requirement, liquid effluent impoundingareas, Hazardous chemical wastes dumping area as per statutory requirement, are to be included. Itis better to provide a jeepable road along boundary wall for routine check for big factories andprovision for expansion area for product, and intermediate and steam plants. Procedure for landacquired from govt is lengthy and efforts are to be made early once the approximetely size of landis ascertained. Land acquision is through district collector or magistrate.

(h) Process Check(i) Basic conversion yield. The licensor need to provide data about catalysts type, composition,

operating temperature/pressure, yield, reduction procedure, inert gas requirement for used catalystunloading, life of catalyst recommended, supplier etc. If these are not furnished, the licensor is tobe requested to provide answers to these and other questions. In addition, whether yield is assumedif not full scale testing is done; how much is contingency factor. If scale up has been made in reactordesign and other equipment by licensor, the extent of which should be asked.

(ii ) Thermodynamics. The licensor should give separately, when asked for by operating company,thermodynamics of the process taking its account of the heat of reaction, heat of combustion foreach reaction and overall reaction. The sectionwise heat balance in the overall heat balance of theplant need to be asked from the licensor.

(iii ) Material balance calculation. The licensor often, if agreed to, in agreement, gives the totalmaterial balance calculation which is of course confidential. If the licensor do not agree, then licensoris to be asked to provide calculation for yield rate with raw material input shown in material balance.Process design data sheets for the entire plant should be asked from the licensor during finalisationof the agreement with the licensor. The equipment design calculation data sheets could be asked forfrom the licensor for extra payment if agreed to.

(iv) Fractionation and absorption columns suitability. It is advisable to recheck the designs ofthese columns, using a computer and material balance and other data supplied.

(v) Pressure drop calculations. Check the press drop calculations across packed columns andfractionating towers with available equations or Norton generalised pressure drop calculations.

(vi) Heat exchanger. The film co-efficient (both sides) used as per process equipment datasheets are to be checked.

(vii) Vessel diameter/nozzele sizes. Check vessel diameter as per available data for other plantsusing 6/10th rute and nozzle diameter as per similar data, available from other plants.

(viii ) Check for boiler design based on fuel gas flow and temperature, steam conditions(pressure, temperature), feed water flow and temperature and blow down etc.

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(ix) Instrument Air. The running I.A. compressor (120% capacity) should be steam driven andspare one should be an auto-start electrical driven compressor with emergency power.

Instrument Air is connected to compressed air receiver from which instrument air is sent fordehumidification in a duplex silica gel drier for regeneration, separate electrical driven blower (withspare) and electrical heater (with spare stream heater) need to be provided. Emergency powerconnection is required for blower and electrical heater. The capacity of compressed air receiver andI.A. receiver from drier should be atleast for 20 minutes each respectively.

(x) Raw material and fuel gas system. If N.G. or L.P.G. is used as raw material and fuel gassupply proper knockout drum, with auto drain system, is to be provided. Heating system forknockout vessel or outlet line (drain) is also needed. To be provided for N.G. incoming system.

(xi) Flare stacks. Adequate bottom drain vessel, sliding support and flare ignition system withpurging, are to be provided. All S.V. outlets, handling inflamable gases are to be connected to flarestack header.

For plants, handling ammonia, separate high vent stack is needed. The liquid ammonia knockoutdrum should be steam jacketed at bottom to vaporise liquid ammonia.

(xii) Fire water system. Should be as per standard statutory codes and a constant runningjockey pump for developing pressure of 8 kg/sqcm in fire water header. The stand-by jockey pumpis to be connected to emergency power. A constant bleed from jockey pump discharge is to beprovided to prevent cavitation inside the pump. The diesel driven fire pump should have battery backup for emergency start up when the discharge pressure falls below the preset limit. No. of firepumps and capacity will depend on fire system design.

(xiii) Lifting cranes. All heavy rotating machinery should have provision for E.O.T. cranes ofcapacity for maximum weight of parts of the rotating machines.

(xiv) Waste disposal

(a) For oil in compressors condensate, API oil separate is required

(b) Cooling water blow down– separate treatment for chromium removal is required.

(c) Waste water from plants is to be pumped to waste treatment plant as required.

(d) Incinerator for paper and other combustible material is required.

(e) Disposal of treated effluent through weir for draining to natural streams with monitoringarrangement for flow and effluent constutents (major) are also needed for satisfaction of statepollution control board.

6. INSTRUMENTATION AND CENTRAL CONTROL ROOMInstrument control room is the heart of a process plant. Proper selection of instruments of

reputed maker is a fundamental task for safe and trouble free run of a process plant. The followingaspects need to be checked in process instrumentation.

(a) Flow measurmentsPrimary measuring elements orifice meters, online turbine flowmeters, oval flowmeter and pitot

tubes (for large flow measurements like C.W. flow) and rotameters etc. Proper distance requirementfor differential pressure across the orifice located in straight pipeline section is to be ensured. Theflow is generally transmitted through pneumatic flow transmeters or pneumatic-electrical transducer

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to central control room. Site indication of flow is often required for process control. The flowcontrollers in control room through actuators are to send electrical pneumatic signal to control valveto position for process requirements. The flow controllers can be set at manual or at auto positionafter setting the set point of the controller. Alarm annunciator is actuated when flow is lower orhigher than the set point.

(b) Pressure Measurements

Primary pressure measurement element is spiral or helical Bourdon tube of required material tosuit process fluid. For pressure, lower than 0.5 kg/cm2 bellow, diaphragms are used. The pressureis transmitted through pneumatic transmitters or pneumatic-electrical transducer to the pressurecontroller in control room. The pressure controller sends controller out put pneumatic signal tocontrol valve as per process requirement. The controllers can be operated manually or can be keptin auto operation at set point beyond which an alarm circuit will be actuated in alarm annunciatorpanel. Separate pressure indicator is put on the vessel/pipeline for on-site observation. The range ofdial type pressure gauges should be twice the operating pressure, differential measurement of pressureshall be done with bellow or diaphragm type instruments.

(c) Level Measurement

Primary measurement is by float level transmitter, capacitance probe etc. For freezing solution,the level transmitter is normally stem jackated. The material of construction should be carefullyselected to prevent corrosion.

(d) Temperature Measurement

Primary measurement is by resistance thermometer, thermocouples of suitable metals orcombination for the temperature range to be measured. For high temperature, pyrometers and segarcones are used.

Molten metal bath temperatures are taken by H.T. termocouple which is pushed through thebath and finally gets melted. Liquid filled thermometers are used for low temperature indications.Ranges of different thermocouples etc., are as follows :

Resistance thermometer = upto 350°C

Iron constant at thermocouple = 350 – 450°C.

Chrome Alumel thermocouple = 450 – 850°C.

Locally mounted thermometers upto 8 m in distance from impulse point shall be dial typesbimetallic.

Electro/pneumatic Transducer type transmitter and final control valve, pneumatic type are usedfor temperature control.

(e) Controllers

The modes of controllers shall be carefully selected depending on process requirements. Generallytemperature controllers should be 3 modes types (percentage, proportional and resets and rate) withauto reset. The flow controllers, level controllers and ratio controllers could be 2 mode controllers(percentage proportional and reset) with auto reset. The pressure controller can be either 2 modeor 3 mode controllers depending on criticality of operation. Controllers should have automanualchange over. The control points of controllers may be 0.75–0.80 of full scale range (i.e., 75–80%).Reset mode is required for precesion control with adjustable sensitivity.

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(f) Control ValvesThere are various types of control valves i.e., self acting, remote operated automatic control

valves, direct or reverse acting, with pneumatic diaphragm control valve, solenoid operated controlvalve or electric motor operated control valve. The valve port type is double seated with suitabledesign for lower pressure on valve glands. Hand wheel in control valve is required under thefollowing conditions. (i) where there is no bypass or block valve (ii ) In 3-way valves and valvesunder special services. However, no handwheel is provided in emergency control valve. Control valve

of size above 1

2" shall be of single seated type. Valve positioners are provided when the valve size

is 1

22" and above. Valve positioner in control valve is required for the following conditions :

(i) Butterfly valves of size 4" and above. These valves have low pressure drop.

(ii ) Temperature control valve above 200°C operating temperature.

(iii ) When distance from controller to control valve exceeds 50 metres.

(iv) Control valve with extra deep gland packing.

(v) Double seated control valve of size 4" and above.

(vi) Single seated valve of size 2" and above.

(vii ) For services where close control is required or hunting is to be avoided.

(viii ) Where control valve requires valve positioners, they should be of force balance type.

(ix) Special purpose relay or volume booster may be incorporated into the control loop toovercome lagtime or to accomplish special control functions.

(g) Flow Through Orifice Meters

There are various empirical equations for orifice flows which incoporate a correction factor.Correction factors for steam and gas orifices are given below :

Steam Orifice, KSSM

SD

= ρρ

where, KS = Corrector factor

ρSM = Steam density at operating condition.

ρSD = Steam density at design condition.

Gas Orifice, M D D

GD M M

TK

T

ρ ρ= × ×ρ ρ

where, KG = Gas correction factor

ρD, ρM = Pressures at design and operating conditions.

TD, TM = Temperature at design and optg. conditions.

ρD, ρM = Gas desnsities, design and operation conditions.

(h) RecordersGenerally 12 point recorders are to be used in control room or field (if necessary)

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(i) Instrument air receiversThere should be atleast 20 minutes storage of instrument air at 8 Kg/sqcm and dew point of

–40°C. The instrument air receiver should be divided into 2 or 3 storage vessels for various sectionsfor safe shutdown due to power failure. Pneumatic instruments generally operate upto 2.5 Kg/cm2

air pressure at the instruments. Filters for instrument air and I.A. receiver are to be periodicallydrained.

(j) Online instrument analysers(i) Condensate coolers in gas sampling point with drains are to be provided before gas flow

to electrodes for analysers. Air conditioners are generally required for sensitive analysis.

7. PLANT INSTRUMENTATION(i) Process plants of early 80’s design were usually provided with pneumatic and electrical

instruments (both field and control room) without any shared distributed control system (DCS) withbasic logic diagram for specific control system using pneumatic – electronic transducers for controllersand pressure/flow etc., were transmitted to controller electronically by electronic transmitters. Theworking of DCS using basic logic diagrams and computers is given below:

AI = 17

PAdp/dt

Detail loop of a pressure control system

AO2II Console no . 2 (C– 2 )

(PI)

A.S. P

PY2II

PCV2II

A.S.

AO2II

S im plied P&I diameter forpress control loop

NO 2

PCV2II

PT2II

Fig. 1 Fig. 1(a)

The left side diagram of Fig. 1 would be as it appear in detail P and I diagram and that in theright side diagram (Fig. 1a) would appear in simplied P and I diagram.

The pressure indicating control loop is controlled by a shared distributed control system (DCS).The setting of this conroller is received from a supervisory computer over a shared data highwaythat provides software link between the computer and DCS system. The control loop tag no. 211indicates that it is the 11th instrument on P and I flow sheet no. 2.

On the measurement side of the loop there is an electronic (4–20 mA DC output) pressure

transmeter which is connected to a process pipe line by a 1

2" shut of valve (13 mm) and has a

pressure range of 0–3000 PSIG. The output from this transmeter is received and identified at themultiplexer of DCS system as an analog input no. 17 (AI–17). The controller PIC–211 is located on

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console no. 2(C–2) of the DCS system and is provided with proportional and integral (PI) algorithm.The DCS system also provides a high pressure alarm function PA and a high rate of pressure risewill provide an alarm on this measurement.

The analog signal, leaving the multiplexer in the output side, is identified as AO–211. The signalis 4–20 mA DC signal which is received by a current to air converter (PY – 211) mounted on thecontrol valve. The pneumatic output signal from I/P converter goes to the diagram motor of thecontrol valve. Air supply is provided for both valve positioner (P) and I/P converter.

(ii ) Therefore, (a) process function diagram which gives a site specific logic diagram (b) a Pand I diagram and (c) a hardware diagram giving detail wiring diagram, will constitute the basicdrawings for a process plant. Such set of drawings should be provided by the plant designer.

(iii ) All the above drawings for instrumentation shall be checked thoroughly for any inconsistenciesand process requirements. If Hazop analysis I and II are available, the recommendations should havebeen incorporated in these drawings. Special requirements of emergencies and instruments to tacklethese emergencies should be looked into. Hazop III requirements during commissioning are to benoted for eventual implementation.

(iv) Thermocouple and Pressure elements materials should be checked for compatiability.

(v) Adequacy of field instruments should be checked.

(vi) Data logging computers are provided in DCS systems; printers and voice communicationwith field staff should also be made available.

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Once it is decided by the top management to set up a new project on the basis of atechnoeconomic feasibility report, the estimation of a detail project cost is the next step. Thecost estimation for a new project involves consideration of various factors in detail so as toarrive at the total cost of the project. The major heads are:

1. Preliminary expenses for TEFR, survey, metrological data etc.

2. Land and site development.

3. Civil works cost of factory, plant buildings and auxiliary buildings.

4. Plant and machinery cost including handling and duties.

5. Miscelleneous fixed cost.

6. Cost of auxiliary utility services.

7. Cost of Effluent treatment plant and measures.

8. Design Engineering and procurement charges.

9. Technical know how, process licence, drawing checking fees and royalty (if any).

10. Project management charges including statutory fees.

11. Erection charges.

12. Incidental charges.

13. Erection supervision charges.

14. Commissioning charges including pre commissioning.

15. Interest charges during construction and commissioning.

16. Margin money on working capital.

17. Township, welfare and medical expenses.

18. Escalation or contingencies.

Other Informations19. Typical percentage costs for a new chemical plant and depreciation rates.

DETAIL PROJECT COSTESTIMATION

Chapter

51

298

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DETAIL PROJECT COST ESTIMATION 299

1. PRELIMINARY EXPENSESHere TEFR required survey cost, metrological data acquisition cost etc., are to be included.

Metrology data are important as it is to be included along with other data on site for sending toprocess designer as basic data on site.

2. LAND AND SITE DEVELOPMENTThe quantum of land required for the manufacturing plant/factory for a particular product

selected, is to be ascertained from the process technology supplier or process licensor. For this,process licensor will ask for basic design data viz ambient temperature (Dry and wet, bulb temperature),data on the velocity and direction of wind and water table.

Past earthquake data/seismic group of the area as per relevant IS code – 1893, land contourmap etc. For smaller projects, earthquake data, land contour map (geotechnical map) are usually notrequired. The other data required are:

(i) Soil load bearing capacity, type of soils, flood water levels (minimum and maximum) ofnearby river. If soil load bearing data is not available, test and determine it.

(ii ) Elevation of site and survey data of the site.

(iii ) Availability of basic infrastructure facilities, viz. P.W.D. road nearest to site, its width andthe condition of road, H.T. power supply nearest point, either substation or H.T. transmission line,fax, telephone/e-mail facilities.

(iv) Nearest drainage canal for surface water and factory, treated effluent discharge, availabilityof any river or irrigation canal nearby.

(v) Availability of skilled and semi skilled labour.

(vi) Nearest town and public transport availability for going to site.

(vii ) Type of land available in the area, agriculture, homestead and barren.

(viii ) State/central Government policy on location of industry.

(ix) Distance from nearest rail head and marketing zone location.

(x) Pollution norms both air quality and water limits for the type of industry planned.

(xi) Bulk power supply rates and cost of laying H.T. transmission line to factory substation,H.T. voltage availability.

(xii) Municipal water supply availability and analysis of water. River water analysis and distanceof river water from proposed site. Tubewell water analysis in the area.

The land and land development cost shall include the following

(a) Current market rate of land

(b) Legal fees for 13 year search of proposed land area holdings and conveyance charges.

(c) Cost of macadam metalled roads (min 5m wide) to site from P.W.D. road.

(d) Survey and site levelling cost.

(e) Cost of factory 5–7 m wide internal semi pucca roads with approach roads, culverts andpucca surface drain.

(f) Barbed wire fencing/boundary wall construction. cost.

(g) Main gate with security post and barrier cost.

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(h) Cost of temporary office shed, godowns and hard core open space for storage of equipmentand plant stores.

(i) Initial tubewell boring cost for site construction and temporary overhead tank.

(j) Cost of initial temporary surface water drains from site to outside discharge point.

3. CIVIL WORKS COST FOR FACTORY AND AUXILIARY BUILDINGSTotal civil works cost to be determined for the following heads.

(i) Main plant factory civil works and cost of structurals.

(ii ) Auxiliary plant buildings for utilities plants. Safety office, plant laboratory and central lab,Fire service, rest room, river water pump house or Tubewell battery cost, cooling tower cost andover head tank.

(iii ) Administrative building, plant offices and canteen.

(iv) Factory effluent treatment works and Air quality monitoring station.

(v) Cost of finished product storage, raw material storage, warehouse for plant stores are tobe included.

Once the plant process design is completed and plant designer have furnished the preliminaryplant layout drawings and civil scope drawing, civil works cost against the above heads are to bedetermined as per local area civil construction rates. The cost of AC, electrification for roads andbuildings, Air conditioning of control rooms are also to be ascertained. Doors and window are reqd.to be of steel construction with glass panes and minimum height as per factory Act. Toilets costsalso have to be included. FI’s have specified civil construction rates, there rates also to be checked.Escalation cost @ 10% to be considered.

4. PLANT MACHINERY COST(i) Main and Auxiliary Plants

Once the plant designer or Technology supplier had finalised process design and factory layoutand duly approved by plant authority, the basic data sheets for static equipment and moving machineryare available, project authority is to invite quotation from reliable and reputed equipment suppliers.Based on their quotation rates, cost of plant and machinery are worked out. For urgent evaluation,when quotation is not available, cost is usually evaluated by 6/10th rule which is applicable whencost for other sizes of the same equipment is available.

For selection of a particular process, offered by the plant designer, after basic design data of siteis sent to them, the following factors are to be considered.

(a) Consumption norms for raw materials, utilities, raw materials and, product/by-productspecifications. This is to be compared with data available from other plant designers for betterconsumption norms and product quality (usually a M.O.U. is executed with the plant designer earlierwhich detail out the scope of work, etc. of both plant designer and plant authority/consultant.)Instead a contract document could be signed.

(b) Availability of raw materials indigenously of particular purity, specified by plant supplier orto be imported.

(c) Number of operating personnel required for each main plant under this scope.(d) Whether the process, to be supplied, is the latest one, requiring lesser equipment and

operating personnel.

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DETAIL PROJECT COST ESTIMATION 301

(e) Technical know-how and supervision charges of the technology supplier. If royalty isinvolved this is to be within the limit of present tax laws.

(f) Nearest port distance and mode of import.

(g) How many plants of similar or of higher capacity, are working else where and their addresses.

(h) Plant designer to provide 10–15% excess capacity margin in equipment supplied.

Only sophisticated/patented equipment are imported and other equipment are procuredindigenously.

The process of evaluation of cost of plant and machinery is a time consuming affair. All costof moving equipments specified, including commissioning and 1–2 year spares. Fi's do not insist forlowest quotation rate and cost heads are given as imported (items) and indigeneous rupee cost. Ifthe imported items are listed in OGL group of current import export policy book, the payment canbe made in Indian rupee and if not payment is to be made in F. C. The cost, insurance, frt, C.D.,port handling and transport cost is to booked in appropriate heads of project estimate. For loanassistance of F.C., the imported item cost, CIF value to be separated out for F.C. loan. Considerthe piping, insulation painting material costs for main and auxilation plants.

For auxiliary utility plants, the quotation is usually invited from indigenous plant suppliers withdetail procurement specification of equipment.

5. MISC. FIXED COSTS(a) D. G. set of required capacity as per plant designer's requirement with extra 25%. Cost

of commissioning by supplier to be included.

(b) Yard piping cost for process materials and utilities

(c) Laboratory testing items for main and plant lab.

(d) Electrical cable and from main substation to plant substation. The transformer and relayspanels, bus section; all MCCs to have single/3 phase thermal over load relay of reputed manufacturer.

(e) Cost of outside H.T. transmission line from nearby transmission line to proposed sitesubstation etc. H.T./400 volts AC three phase, 50 cycles Hz transformer. All the cost should includeconstruction with spares for 1–2 years spares. D.G. set cables cost to be included.

(f) Insturmentation cost for main plant including instruments cables etc., and spares.

(g) Cost of all lab. testing items and commissioning cost by supplier for critical items.

(h) Fire protection item (fire extinguishers under ground fire hydrant lines, nozzles, fire housesitem, fire alarm siren, fire pumps, (one operating + one spare booster pump).

(i) Transformer oil filter.

(j) Railway siding (if any) cost, cost of special wagon if ODC consignment are there and ashunting engine usual norm for P and M cost is to take 5% escalation for firm quoted items and10% escalation for non firm estimated cost.

6. COST OF AUXILIARY UTILITY SERVICESAuxiliary utility plants viz. steam generation, D.M. water plant, process water treatment plant,

Tubewells and pipeline cost to process water plant, sanitary water distribution line, cooling towersare required to be calculated judiciously in order to give suitable excess capacity margin, usually20–25%.

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(i) Steam generation plant: D.M. plant and P.W.T plant based on available fuel (N.G., fuel oilor any other available by-product fuel gas); various turn key suppliers quote for these items basedon client’s capacity, steam conditions, super-heat and quality requirments.

Once the process designer had firmed up utility consumption norms and accepted, quotationsare to be invited from reputed S.G. plant supplies. D.M. water quality required is given by S. G.plant manufacturer based on which, quotation for D.M. plant is to be invited. The capacity requiredfor S. G. plant should be about 20–25% excess, and co-generation of power also is to be consideredby extracting heat from flue gases from SGP with auxiliary firing in big projects. The D.M. watercapacity will include SGP requirement plus quantity for other main plants (if any). DM plant is acritical plant and all technical details are to be asked for. The plant should have adequate instrumentationfor manual/auto operation for change over, silica analyser, pH meter, flow meter etc. Also gravityfilters, deoxidiser for process water intake, condensate polishing unit (cation exchanger) etc shouldbe available. The storage capacity of D.M. water tank should be for minimum 20 hrs or so. Theselection of ion exchanger resins depends on the quality of process water which should be free fromorganic impurity. D.M water plant quotation is asked for after quotation for process water treatmentplant is received and before issuing P.W.T. plant quotation the specification of process water availableat site (either tube well, river/canal water or municipal water) to be finalised and included inquotation, giving the capacity and raw water feed quality to P.W.T plant.

(ii ) Cooling tower and pump house – The cooling tower capacity, C.W. Hot/cold welltemperatures, D.B. and wet bulb temperature are usually fixed by process plant suppliers based onthe basic site design data given to them as per design process requirements. These towers are usuallyinduced draft cooling towers with 2 speed fans at the top and top deck distribution lines, with plasticnozzles for hot water falling into the tower having glass reinforced wooded grid supports andasbestors louvre. The construction of tower is either of treated wood or concrete. The tower isdivided into cells depending on cooling water flow required the cold well outlet is usually providedwith screens (1 + 1) to remove any foreign material going to cold well pump suction; with provisionfor purge water valve pit for each cell.

C.W. Pump house – The capacity and discharge pressure with floded suction of C.W. pumpplus spares to be decided carefully so as to provide return hot cooling water to flow upto the topof cooling tower. Emergency cooling water pump of adequate capacity with D.G. set power isrequired to be provided.

The layout of cooling water header and branch headers to different sections of a plant is tobe suitably planned and header branch lines sizes are determined to cause minimum pressure dropin the C.W. circuit.

As per Casey rule, the summation of pressure drops in the outgoing and return circuits shouldbe zero or nearer which requires vigorous pressure drop calculation for flows in each line. Excessmargin of 15–20% should be considered in flow calculation.

7. COST OF EFFLUENT TREATMENT PLANTSEnvironment protection requires effluent treatment for water and air pollution which is mandatory

for all types of industries. The state pollution board should be initially asked to give the staterequirements. The state requirements often is the same as per MINAS/IS or even stringent for finaldischarge point concentration of pollutants. It is also depend on the type of industry. The waterdischarge quality after treatment should be as per water prevention and control of pollution Act 1974(central)/state act.

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The process designers usually give the discharge quantities of pollutants from each plant (mainor auxiliary). As per present day, PCB requirement is given for even condensate blow down fromsteam boilers, open condensate drains are to be separated by separate lines and collected in headersand sent to effluent treatment plant. The treated effluent discharge, coming from various industriesis specified in environment protection Act-86. Air quality discharge limit of pollutants is given in thecentral Air (prevention and control of pollution Act-1981 which is given below.

Table 1Ambient air quality

Area Category SPM SO2 CO NOX unit = µg/m3

A Industrial and mixed use 500 120 5000 120

B Residential and rural 200 80 2000 50

C Sensitive 100 30 1000 30

N.B. New item: RSPM – Respiratory suspended particulate matter. MINAS or minimum nationalstandards for limits of water and air pollution, is as per above act as well as EPA act rules 1986.EPA rules 1986 defines the sound decibel limit in work places as follows.

(i) Continuous sound level = 65 db

(ii ) Sound level for short duration = 90 db

Sound level measurement at 2m distance from source. Also in steam generation plant use ofESP is mandatory for a certain capacity.

While asking a manufacturer or supplier to quote for plant facilities, it is always better to givethe above pollution standard (Air and Water) along with expected water and air pollution concentrationsas per plant suppliers. The effuluent plant supplier is to meet the EPA standard or MINAS standardor state PCB standard.

The total cost of liquid effluent treatment plant will include:

(i) Cost of C.T. purge water treatment facility to reduce Cr+6 to Cr+3 if chromate–phosphatetreatment usually 10 : 20 ppm is contemplated for anticorrosion measure.

Note : When Phosphorate based anti-corrosion treatment is considered only delay chamber forpurge water storage is to be provided.

(ii ) Cost of neutralisation tank (rubber lined or epoxy coated) for D.M. plant regenerationwaste water (H2SO4 and NaOH).

(iii ) Cost of bulk effluent treatment plant for specified plant effluent coming to ETP either viaa pump or separate utilities effluent drainage line from main plants.

(iv) Cost of delay ponds (1 + 1) for treated effluents for 1 to 2 months storage capacity.

(v) Flow measuring weir and cage for fishtest for liquid effluent discharge to canal, river,nullah should be included in cost along with all specific instruments, analyser etc.

(vi) Cost of electric installation of the E.T. plant building electrification, etc. to be taken.

(vii) Cost of special concrete dumping pit if harmful effluent like arsenic etc. are to be handledas per Hazardous materials handling Act-89.

(viii ) ASTM oil separation (with coke) cost for each plant and SGP plant.

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(ix) Cost of oil centrifuge for emulsified turbine oil.

(x) Cost of central lab instruments for special analysis of water and air pollution.

7.1 Cost for Pollution Abatement SchmesThe air quality in the plant should be as per table –1. The plant designer should be asked to

keep the stack emission minimum so that the above norms can be kept in the ambient air. Thedesigner is to provide filters for dust emission, SO2/NOX scrubbers in the main plant it self. COemission from stack beyond the limit as per table – 1 is not allowed. It causes headache at higherconc. in air. Unlike water pollution abatement schemes, air pollution control equipment are installedin the plant which generates the pollution.

7.2 Air Pollution Cost of Equipment Including Monitoring Instruments(a) Cost of one ambient air quality monitoring station.

(b) Cost of scrubbing, if any, for air pollution control.

(c) ESP for steam generation plant (if applicable).

(d) Cost of wind velocity and wind direction indicator.

As per SMPV Act/rules cost of emergency shut off valves (remote controlled) are to beinstalled for Hazardous storage like liquid NH3 spheres. Also the cost of commissiong spares and1–2 yrs spares are to be included in all effluent treatment plants.

8. DEP CHARGESBased on quotation from plant designers/ consultant, design and engineering charges are to be

included. For procurement of equipment and machinery, it is either done through consultant/firm orby the client itself, in the latter case stage wise inspection or final inspection by competent/agencyis required to ensure that the equipment conforms to specification issued by consultant/client/designer before shipment. For foreign supply usually Lloyds registrar does it at a fee which is tobe included in procurement cost along with indigenous items inspection cost. Usually DEP chargesrange form 15–20% of project cost.

9. FEES FOR KNOW-HOW, DRAWING CHECKING, PROCESS LICENSE ANDROYALTY CHARGES

These costs are usually mentioned in aggrement with technology provider for complete patentedprocess of manufacture, royalty is to be paid which should be within the limit specified in Indiantax laws. Know-how charges is for complete design package and License fee is for use of anypatented process.

10. PROJECT MANAGEMENT CHARGES INCLUDING STATUTORY FEESThese charges include all site expenses for salaries of employees, establishment cost, stationary

and postage, Telephone and fax, Company vehicle/hired vehicle maintance and fuel cost, wellfare andmedical expenses, bank charges, electricity and water charges, local taxes, tour expenses, Guesthouse (if any) expenses. Gardening and cleaning expenses, office furniture and equipment expensesetc. All statutory costs for CCE licence, fire licence, electrical licence. etc., are to be considered.These costs are to be taken upto the end of commissioning period and before start of commercialproduction.

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11. ERECTION CHARGESCosts based on quoted prices of erection contracts for equipment, piping and vessels for

mechanical items, electrical and instrumentation items. Turn key supply cum erection contract valuesfor certain items are also to be included. NDT tests cost also to be included. Every erection contracthas a standard clause for escalation based on consumer price index for industrial workers. For big/medium/small projects, certain provision for delays due to reasons attributable to project owner'slapses is better to be included in erection cost. Insurance cost of erection to be included.

Hiring of construction equipment charges, Training expenses, Salaries and benifits provided byCompany to site staff/other offices and income tax on foreign supervision is to be included.

12. INCIDENTAL CHARGESThese charges include ocean freight, railway and road transportation charges, Insurance, Inland

handling at port transhipment cost which is applicable to customs duty, excise duty, state/centralsales tax. The typical rates are as follows:

Inland handling and transportation = 6% of FOB for cost of equipment and supplies

Ocean freight = 15% of FOB

Customs duty = depends on type of industry (usually 20%)

Port charges = 2% of CIF

Excise duty = 15–20% of FOB (usually)

Central sales tax = 4% against C form

Insurance = 2% of delivered cost of equipment and supplies.

13. ERECTION SUPERVISION CHARGES.Supervision charges for vendors of equipment including foreign equipment, erection supervision

charges of foreign personnel, Income tax liability of foreign personnel and charges for supervisionby consultant engineers, travel expenses ( to and from) for both vendors engineers and foreignsupervision including air fare, car rental for road travel etc.

14. TOWNSHIP, WELFARE AND MEDICAL EXPENSESFor few senior personnel and minimum Technical essential staff it is advisable to have a small

township for which cost of land, civil works, O.H. electric supply, roads and drainage, factorydispensary (where applicable), ambulance and other facilities costs are to be considered. Bus facilityfor staff also to be included. Commissioning expenses based on commissioning schedule as per barchart/P E R T or C P M charts, cost of commissioning expenses is to be determined. The variablecost of raw materials and utilities, plant stores, packing materials, maintenance materials. Insuranceand taxes and selling, administration expenses and contingency.

On the total of above cost, debit the cost of finished product produced during commissioning.

15. MARGIN MONEY ON WORKING CAPITALMargin money is paid by banks–workout the working capital required at 100%, 90% and 80%

loads. 25% of annual total working capital requirement will be margin money. The sale price ofproducts is to be correctly determind. The cost of packing material, chemicals and consumables,product inventory assumed, goods in process, cash balance in bank, accounts payable deposits and

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advances are to be considered. In other form of FI’s norms margin money is calculated based on(1 – 4) months requirements raw material and consumables, finished goods, 1/2 month receiveable,1 month salary and other expenses, one month period and imported raw materials for 4 months.

16. INTEREST DURING CONSTRUCTION PERIOD ON BORROWED CAPITALBased on debt equity ratio, the financing charges during construction period is to be ascertained.

Initially equity amount is spent as it is a low cost capital. After expenditure of equity amount,calculate subsequent years interest at prime interest rate prevailing as per term loan condition of FI’s.Assume loan amount is received at middle of the year and calculate interest there on.

17. ESCALATION OR CONTINGENCIESConsider 5–10% escalation cost or contingencies

OTHER INFORMATION

18. PERCENTAGE COST OF A NEW CHEMICAL PLANTItem Range of Cost

Civil works ... 10 – 30 %

Equipment ... 50 – 60 %

Piping ... 15 – 30 %

Electrical ... 12 – 20 %

Instrumentation ... 8 – 20 %

Depreciation rates

Civil works ... 4 % (25 yrs)

All others ... 10 % (10 yrs)

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TYPES OF CONTRACT

Chapter

52

1. There are several types of contracts. Broadly the contracts can be classified as given below.

1.1 Contractor will do consultancy, design, engineering and procurement. Erection by others;precommissioning and commissioning by owner with supervision by consultant.

1.2 Owner will supply basic design data viz soil bearing load, cooling water parameters, dry andwet bulb temperature, wind conditions etc., and contractor will do design, engineering,procurement, erection and commissioning. This is also called turn key contract.

1.3 Owner will do design, engineering and procurement and contractor will do erection andcommissioning by owner.

1.4 Owner will do process design only and contractor will do detail engineering procurement anderection. Commissioning by owner.

2. In case of plants where foreign technology is involved and when a contractor/consultant isinvolved, a memorandum of understanding between owner and contractor/consultant is to beexecuted where in detail scope of work by both parties are specified along with fees. Theconsultant/contractor usually executes an agreement with foreign technology supplier, givingdetail scope and supply of technology and prices of each activity including know-how fee, detailengg. checking of drawings by consultant etc.

3. Mode of re-imbursement to a contractor/consultant is an important parameter for legal andbusiness point of view of a contract. There are four different types of re-imbursements asfollows.

3.1 Cost Plus ContractThe contractor is reimbursed for all costs applicable to the contract, plus a percentage of the

cost for overheads and profit.

3.2 Cost Plus Fixed Fee ContractThis is similar to Cost plus contract except that the contractor can only earn a specified fee.

All other payments are reimbursed for direct cost only. There are many variations of this type ofcontract.

3.3 Lump Sum Fixed Fee Price ContractThis contract allows only a fixed sum of money nothing more or less than the fixed fee. Here

all contract contror's services are detailed out by the owner in the NIT; escalation clause may ormay not be there. This contract has the scope for dispute.

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3.4 Guaranted maximum ContractThis is similar to lump sum fixed fee contract except that the guaranted price may apply to

material (and labour) only; escalation on either material or labour may be allowed. In such contract,contractor is allowed a bonus depending on amount of charges for earlier execution.

3.5 Unit Price/Item Rate ContractHere all types of work involved are itemised and payment is as per item rate quoted.

4. EXCALATION CLAUSES IN A CONTRACTThere are various factors in a contract where escalation is to be paid to contractor due to rise

of consumer price index for labour, delay in handing over the site and site facilities like power, water,shed (if applicable) etc., delay in handing over of equipment for erection, erection materials (underowner's scope), delayed payment etc.

4.1 Penalty Clauses in a ContractOwner usually put conditions for imposing penalty as liquidated damages for delay in completion

of a contractual time period. Often failure to provide Bank guarantee in time by the contractor ispenalised. The liquidated damages in failure in performance to meet rated capacity and specificconsumption norms as per contract invite penalty for not meeting the guaranted norms, as per ratesspecified in contract.

5. A contract document can be executed with the selected contractor and broadly should includealso the following:

5.1 Effective date of contract

5.2 Name and address of parties, legal definition and act authority.

5.3 Acknowledgement of engineers knowledge in undertaking the project and inview with the client.

5.4 Nature and extent and character of the project and time table.

5.5 Service to be rendered by consultant.

5.6 Service to be rendered by client.

5.7 Provision of termination of contractor's engineer’s services before completion of work.

5.8 Competence of engineers in services rendered.

5.9 Method of payment of account, interim payment and final payment in full settlement.

6. PROVISION FOR PENALTIES FOR DELAYED PAYMENT6.1 Provision for change of scope of project – prepn. of alternate drawing, if desired, drawings,

construction documents and details of expenses required.

6.2 Specification regarding what constitutes approved engineers work by the client.

6.3 In addition, the document should contain clauses 4 and 4.1.

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PROJECT FINANCIALMANAGEMENT

Chapter

53

1. FINANCIAL EVALUATION OF A PROJECTThis is an important task to evaluate a project for any manufacturing enterprise or for

modernisation or expansion plans or installing a costly machine.

1.1 I.R.R.This method is called internal rate of return. In order to determine I.R.R. it is necessary to

calculate annual income at production levels of 80% or so starting from O date when financialarrangement or approval is firmed up. This method takes into account the time value of money bydiscounting the future net cash flows calculated before depreciation but after taxes to arrive at thepresent value of net annual cash flows. The I.R.R. is one at which the discounted future cash inflows equal to cash outflows. If this is +ve, the project will not only pay out the total project costbut will also give an annual return at the I.R.R. One important point of consideration is that projectswith larger cash in flows in latter years may be rejected in favour of one generating higher cash inflows in earlier years. In the long term outlook, time adjusted I.R.R. to recover the investment inthe shortest possible time is the best insurance for the investors point of view; subsequently profitsare additional gains.

There are various DCF factor tables. The normally used DCF table is based on half yearlycompounding of interest rate with the assumption that cash flows of each year is received/paid outat midpoint of the year and compounded in half yearly interest periods. For smaller projects annualcompounding of DCF factors can be considered.

Procedure(i) Prepare – expenditure statement for 10–12 yrs at 80% production level and considering

increase in short term (upto 1 year) borrowing so as to arrive at the net income (cash in flows).Consider equity receipts but do not consider depreciation and interest.

(ii ) Incorporate the year-wise project cost expenditures made from DPR in the I.R.R calculationtable, till the told project cost less foreign currency expenditure (if any) is fully neutralised for theduration of the project implementation period starting from first year.

(iii ) Put the net annual cash inflows yearwise thereafter in I.R.R calculation table.

(iv) Discount each years cash flows at appropriate DCF rate which is usually the Co.’s cost

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of capital rate at two adjacent DCF factors. Calculate the discounted cash inflows for each discountfactor for 10–12 years.

(v) Add the two discounted values separately.

(vi) Substract the total 2nd discounted value from the total of 1st discounted value. Thedifference of discounted value will give the cash inflows for 1% difference in discount factors.

(vii) Divide the total of discounted value (+ve) of 1st discounted value by the difference indiscounted values as per (v) above. The factor thus obtained is less than 1.

(viii ) The required I.R.R. is the 1st discount factor plus the quotent factor of (vi) above.

(ix) If the minimum rate of return or total capital employed is near or equal to the I.R.R., theinvestment should be made.

The ROC/ROR should not be less than the I.R.R.

(x) The detailed cost heads for net cash inflow is given in table-III.

2. COST–BENEFIT ANALYSISAnother time adjusted capital budgeting technique is the benefit cost ratio (B/C ratio) or

profitability index. Often B/C is generally called cost benefit analysis. This approach measures thepresent value of returns per rupee/ doller invested. This can be said to be the ratio which is obtainedby dividing the present values of future cash inflows by the present value of cash outflows.

Table 1

Project CostYears Cash outflows Discount Discounted

factor cash outflows

1

2

3

..

...

12

Total

Benefit (after commissioning)Table II

Years Net cash inflows Discount Discountedbefore depreciation factor cash inflowsbut after taxes

1.

2.

3.

..

12.

Total

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Benefit–Cost Ratio = Total present value of cash inflows

Total present value of cash outflows

This ratio should be over 1.10 (min.). Discount factor table for annual compounding for onedoller (or Re) at the end of n years is usually considered.

3. PAY BACK PERIOD (P B P)This is a traditional method of appraising an investment option and answers the question as to

how many years till the project takes to pay back the original cost of investment. The methodprovides the no. of years over which the investment will be recovered or paid back from cashinflows. If the pay back period is quite lengthy or equal to or little less than the prime period of theproject, it is clearly unacceptable.

Pay back periodTotal investment

Net annual cash flowsP B P)=

(

Here profit should be taken before charging depreciation but after deducting taxes. As investmentwill include long term loans; interest there-on shall be allowed to arrive at the net profit (i.e., net annualprofit after interest and taxes). Since time adjusted money factor is not considered in this method itis a crude method. The situation can be greatly improved by applying the discount factor in thedenominator. Shortest the P.B. period, better is the project economics. Subsequent period of economiclife of the project of the period goes to the advantage of enterpreneurs. The technique may be appliedto check whether the PBP is less than the predetermined PBP set by the management for acceptanceor rejection of any project. It is, therefore necessary to determine the present value of cash flows foreconomic life of project and the shortest PBP out of the economic period. This approach takes careof major shortcoming of traditional method and easy to understand for practical application.

4. RATE OF RETURN VS COST OF CAPITAL AND OTHER ANALYSISIRR has to be comparable to required rate of return (RRR). Acceptability of a project depends

whether or not IRR exceeds RRR. RRR has a direct bearing on the cost of capital. Capital iscomposed of different elements viz equity capital, preferance share capital and long term loan capital,meaning thereby components based on different sources. Obviously, each component of capital hasits cost different from each other. The component which takes the maximum risk is naturally thecostliest source of capital. Averaging the cost for all components on weighted basis may be said tobe the rate of the cost of capital. Such capital is popularly known as capital employed.

Cost of capital is a major factor used in financial analysis. For a company to survive the returnon capital invested must not be less than cost of capital. For growth the return must be at least 1%more than the cost of capital. Profit as per percentage return on capital should not be compared withthe DCF yields and instead, a comparison of DCF yields with the rational cost of capital will givebetter result.

Required rate of return. This can be said to be the cost of capital employed. Capitalemployed is a mix. of owner's fund debt capital. Since debt capital is less risky from the point ofview of lenders, the contributors in equity bear the risk of investing money. The ROR for suchinvestors depends on various factors like average industry return, expectation in value of stock, waitperiod in divident pay out etc., RRR, is therefore, the weighted average of cost of debt capital andexpected return desired by owners on their investment which is higher than the going rate of intereston debt capital.

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Profitability index PIThis is usually important for plants after commercial production starts. Discount @ I.R.R. for

cash inflows and outflows for 10–20 years @ cost of capital.

P.I. = Present value of cash inflowsPresent value of cash outflows

× 100

It is also defined as the rate of compound interest at which Co’s outstanding investment isrepaid by profit from the plant or project.

5. BREAK EVEN POINT (BEP)It is the percentage capacity utilisation point at which all fixed cost and variable costs of

operation are recovered.

A. Variable Cost (V)(i) Raw materials

(ii ) Labour cost

(iii ) Utilities

(iv) Packing material

(v) Interest on working capital

(vi) Contingency

Sub total

B. Fixed Cost (F)1. Supervisers and Manager's Salaries, and wages.

2. Over heads

3. Consumable stores

4. Insurance and local taxes

5. Depreciation

6. Selling and administrative expenses

7. Contingency

8. Interest on long term debt

9. Spares and maintenance material

Sub total:

C. Annual Sales Realisation (S) from Products Sold

Therefore,

(i) Break even point F

S VExcluding L.T. loan)=

−(

(ii ) Cash Break even point = F Int. charge

S V(Considering L.T. loan)

−−

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PROJECT FINANCIAL MANAGEMENT 313

Additional Under Break Even PointWhile estimating Cost–Volume–Profit analysis, certain assumptions are made:

(1) Cost behaviour: It is assumed that costs of the firm are divisible into fixed costs andvariable costs. While fixed costs remain unchanged, variable cost vary directly with the level ofproduction.

(2) Unit selling price remains constant.

(3) There is no change in capital structure.

As BEP is the no profit no loss situation, the aim should be to go for projects whose BEP isat low capacity utilisation so that the margin of safety is large.

(4) BEP Calculation is usually made at 80% production level. Depreciation is often not considered.

6. CUT OFF POINT OF COST OF CAPITAL OR MARGINAL COST OF CAPITALCut off point of cost of capital is the weighted averge of after tax rate of interest at which

a firm is able to borrow and the rate of earning on its equity capital which will give stable pricesof the firm's shares in the market. A company tries to use 1st the cheaper form of capital whenthe cost of capital from debt instruments is higher. The cut-off point of available capital is reachedwhen no more equity can be raised. This point of cost of capital is called cut off point of cost ofcapital or marginal cost of capital.

Example: A Co’s capital structure is as follows:

8% debentures = Rs. 20 lacks

Equity, Capital (Rs. 200 per share) = Rs. 60 lacks

Rs. 80 lacks

The market price of each share is Rs. 300 and E P S 20 (after tax). Cost of capital assuming34% income tax rate.

Say, 4% income tax rate on Rs. 20 lacks = Rs. 80,000

and 30% on Rs. 60 lacks = Rs. 18 lacks

tax on Rs. 80 lacks : Rs. 18, 80,000

Cost of capital = 18 80 00080 00 000

100, ,, ,

×

= 23.5%

The conclusion is that, if the company keeps the present debt/equity ratio, it should not investin any projects whose rate of return is less than 23.5%.

7. THERE ARE TWO APPROACHES TO ASCERTAIN THE RETURN ONCAPITAL

(a) Return on capital employed (ROCE)

ROCENet profit after tax Interest onlong term loan

Capital employed× 100= +

This approach shows the benefit provided by the project on long term liabilities plus ownersequity. If ROCE is greater than RRR, there is acceptability of the project.

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(b) Rate of return on equity (ROE)

Net profit after interest, tax pref. dividendROE × 100

Owner's fund (equity holding)

+=

In a sense, equity share holders are the real owners and they take all risks and participationin management, though they have insignifant role.

The ultimate profitability is judged by the above two criteria.

(c) Rate of return (ROR) = Profit before depreciation , interest and taxes

capitalemployed

(For average rate of return, work out cash flows for 10–12 years period)

Table III

Sequence for Determining Cash Flow in IRR/NPV1. Determine annual sales realisation.

2. Deduct variable cost to arrive at contribution.

3. Deduct all factory expenses for conversion cost excluding depreciation.

4. Deduct selling and administrative expenses.

5. Consider increase in S. T. loan during construction.

6. Consider equity as gross receipts if applicable.

7. Consider contingency provision.

8. Financing charges are not to be considered.

9. The resultant value will give the gross cash flows.

9. OTHER FINANCIAL TERMS9.1 Compound Interest

It is the interest on any previous year plus interest on the principal. Formula:

C. I. Amount, A = Po (1 + r)n

Where Po = Principal, r = Compound interest rate yearly.

A = Amount, n = no. of years.

N.B. = For half yearly compounding interest rate = r/2, Quarterly = r/4.

9.2 Simple InterestIt is the interest paid only on the principal borrowed or lent.S. I. Amount, A = Po.r.n

Where Po = Principal, r = Simple interest rate,

n = no. of years.

A = Amount.

9.3 Annual Balance Sheet and P and L Accounts of a Company(i) Gross block = Total fixed assets

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(ii ) Net block = Total fixed assets less depreciation.

(iii ) Net worth = Paid up Equity + Pref. Share Capital + Reserves and surplus– Dr. balance of P and L A/C and Deferred Revenue Expenditureor Net Block + Working Capital – Long term liability.

(iv) Capital employed means net fixed assets plus net working capital (net current assetsexcluding provision for gratuity less net current liability).

(v) Capital structure as per debt/equity ratio. A high debt company has more debt.

(vi) Reserves and surplus value.

10. TERM LOANIt is usually given by FIs. The loan is for over 1 year period. On variable interest rates

depending on type of company. Big corporates usually get term loan on prime interest rate for newproject, modernisation and expansion.

10.1 Fund ProvisionLong term loan to a borrower company for a new project:

There are 4 mazor funding techniques in a S. S. I., medium and large industries followed byFIs.

10.2 Debt/equity Ratio (D/E)S. S. I. = 3 : 1 or 2 : 1 (P and M Limit for S. S. I. = Rs. 3 crores)

Medium and large industries = 1.75 : 1 or 2 : 1.

In a Government undertaking, the debt equity ratio is 1 : 1. Higher debt equity ratio meanslower term loan which reduces promoter's contribution. Debt equity ratio is also governed by debtservice coverage ratio (DSCR). But higher debt (loan) also increases the D.S.C.R. D.S.C.R. shouldbe 1.5 to 1.75. FI's often change these ratios.

It is from the cash flow statement that the DSCR can be determined as per scheduledrepayment of loan and interest instalments. Central subsidy, depending on category of area, variesfor Rs. 10–25 lacks. G.O.I. varies the central subsidy from time to time.

10.3 Promoters contributionIn a public limited Co. promoters contribution is determined based on location of the project

in category A (most backward), B (medium backward) or C (least backward) areas and value ofthe project cost estimate by FIs. For projects above Rs. 25 crores promoters contribution is asfollows.

“A” area = 12.5%

“B” area = 17.5%

“C” area = 20%

Nonbackward = 22.5%

N.B. for projects upto Rs. 25 crores, promoters contribution for A category area is 17.5% andrest of the above norms are same. These stipulations are not fixed always.

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10.4 Unsecured LoanFI's insist that unsecured loans and its interest should not be paid by promoters during the

currency of term loan of FI's and as such any unsecured loan is considered subordinate to the loansof FI's. It is better to consider unsecured loan in project financing calculation estimate. Access tomaximum unsecured loan reduces the equity component as it gives more return on equity or dividentwhich enhances Co’s performance. FI’s usually restrict unsecured loan to 20–25% of promoterscontribution. Unsecured loans, usually, thus remain blocked till commercial production starts or cashacruals begin.

10.5 Security MarginIt is an important factor while taking term loan from FIs. It is related to value of project cost

and depends on promoter's contribution and D.E ratio. It is not a legal documents but FIs usuallyasks for this while sanctioning a term loan.

10.6 Other Forms of Short Term Loan for a Running CompanyShort term loan is usually for 1 year or less.

10.6.1 Unsecured Loan ( Contd. ) This loan is provided by banks and corporates only. The loan is generally for short period and

repayment is due within a year. The loan is sanctioned under a line credit, revolving credit or ontransaction basis, subject to credit worthiness of the borrower company. The debt is evidenced bya promisory note signed by borrower giving the time period, amount of payment and interestcharges. The cash flow of borrower should be sufficient to service the debt.

10.6.2 Secured LoansBased on security of land or fixed assets or both, or other forms of security, new Co’s

generally get secured loan from banks and FI’s. The lender see that the company has sufficient cashflow to make scheduled repayment. The lender, in order to reduce risks, asks for security. The otherforms of security collateral may be accounts receivable, inventory or other assets of the borrower.The loan aggrement is signed both by borrower and lenders giving details of security collateral timeof repayment and interest charges and such aggrement is filed in Department of company affairswhich record the transaction for the public to know that the lender has a security interest in thecollateral specified in the aggrement. If loan is not realised, the lender can put up a case in debtrecovery tribunal (or a recent recovery ordinance) who after proper hearing of both sides may allowsale by auction of the collateral to recover the balance loan with interest. For loan against accountsreceivable, the lender considers only the larger accounts receivable in order to determine the size ofloan. The borrower sends a schedule of accounts receivable assigned for the loan to bank. This isa continuous financing arrangement, as the firm generates more receivables, that is acceptable to thelender and more loan could be sanctioned by the bank and old receivables are replaced by newreceivables.

10.6.3 Inventory Loan or Cash CreditIn floating lien system, finished product or raw materials, spares and inventores including

receivables are kept as security and only a moderate amount of advance or cash credit is given tothe borrower depending on the type of inventory which could be sold by borrower in case suchneccessity arises. Usual documentation procedures have to be followed by borrower as demandedby lender banks.

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10.6.4 Chattel (moveable property) mortgage, inventories are classified serially or in other means.This type of inventory can not be sold by borrower unless lender gives consent. In case of repaidturnover of inventories or inventory that is not identified, because of size or other reasons, these arenot suitable for receiving finance from banks on mortgage deal.

10.6.5 Trust Receipt LoanHere borrower keeps the proceeds of sale of inventory in a trust a/c for the lender who partly

finances the loan to borrower. The lender checks regularly whether the sale proceeds of inventoryis repaid to bank for repayment of loan given to borrower.

10.6.6 Ware House (field) LoanThe materials, stored in field ware house by borrower, is kept as a mortgage security for loan

to the borrower against receipt, given by the field ware house company to the bank. A strict controlof inventory in and out is maintained by the field warehouse company. The field ware housecompany may belong to the same company as that of borrower or its subsidiary company. Theborrower is to provide insurance coverage of materials stored.

10.6.7 Terminal Warehouse Receipt LoanHere the ware house receipt loan is given to the borrower when the borrower keeps the

inventory in a public ware house company. As per loan condition, public ware house co. can releasethe collateral to the borrower only when authorised by the banker or lender. Insurance coverage ofinventory has to be done by borrower.

10.6.8 Compensating BalanceBanks often require, apart from charging interest on loan to borrower, also ask borrower to

maintain "demand deposit" balances at the bank in proportion to funds borrowed. Such balance isknown as compensatory balances which usually varies from 15–20% of line credit. The compensatorybalances enhance the liquidity position of the borrower.

10.6.9 Line CreditThis short term credit is offered to borrower on yearly basis subject to renewal after review

of annual accounts of the company to determine the credit worthiness of borrower. The creditworthiness is determined from cash budget which gives the credit requirements. Banks require thatthe borrower company should clean up bank debt for at least 30 days in a year. This arrangementis not a legal commitment by the bank who can refuse loan should the credit worthiness of borrowerdetoriates. However, the bank generally honours their letter to borrower, indicating the amount ofunsecured loan with interest rates and specify the minimum period when the borrower needs to beout of debt from the bank.

10.7 Revolving CreditThis credit, from a bank, is legal document in which banks commit to extend credit to a

borrower company to a maximum amount of unsecured loan giving the interest charges and periodof repayment of revolving credit. If borrower did not take maximum amount of credit, the borroweris to pay an additional commitment fee for the unutilised portion of loan.

10.8 Transaction LoanThis loan is given to borrower by the bank on the basis of a contract which the borrower has

got. The company usually applies to the bank for transaction loan for executing the contract. Bank

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offers such loan after checking the cash flow record of the company to pay the loan within theperiod of execution of the contract.

11. DEFINITIONS11.1 Opportunity Cost

It is the perspective change in the cost structure of production, following an alternate machineor process route, revised raw material specification or change of operation sequence.

Alternate cost – It is a means of determining alternate cost if production is discontinued andresorted to use of purchased item or commodity of production.

11.2 Shell CompanyA company which has ceased its original activity, has few assets but usually has a stock market

presence as a listed broker. The company provides an easy way for a new company to acquire stockmarket quotation by a shell operation or deals with dubious flow of money and is usually locatedin island cities where mainland govt's has no control over the shell company.

11.3 Take Off Stage of a Country

The capital/output ratio and savings ratio each should be at least 10% of national income.

11.4 OTC ExchangeIt serves as part of secondary market for stocks and bonds, not listed in a stock exchange.

It has listed brokers and dealers who buy and sell stocks/securities at quoted price.

11.5 Co SharesEarning per share (EPS) or price earning ratio, P E ratio

=

Net profit after interest, depreciation and taxes +

pref. share dividend if any

Total no. of equity shares.

orshare price

E P S

Price of share = EPS × P.E. Ratio.

11.6 P E ratio should be 10 – 100 or more. P.E. ratio is

100normal profit rate of a co.

Price earning to growth ratio = P.E.

Net Growth of Profit.

P. E ratio is higher where risk is low and vice versa.

A lower P.E. ratio indicates that net profit growth will exceed its P. E. A P.E. ratio more than1 will indicate that the P.E. is higher than net profit growth. Net asset value (NAV) of a MutualFund – it is the total assets of a particular mutual fund scheme less all debts. It is expressed in unitcurrency per unit.

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11.7 Market Value of a Company It comprises paid up equity shares, preference shares, retained earning and appropriated

surplus.

11.8 Real Interest IncomeIt is the interest rate prevailing less inflation rate.

11.9 Whole Sale Price IndexIt is the whole sale markets' trading rates only and without transportation and marketing costs

which is generally 40–50% of whole sale rate.

11.10 Goodwill of a CompanyThis is determined by three methods viz.

(i) Average Profit Method

(ii ) Super profit method

(iii ) Capitalisation method

In method (ii ) Actual profit of the year less normal profit of the year (expected rate) on thetotal capital is employed. The difference between the two profits, as above, is called super profitwhich is to be multiplied by no. of years of purchase of the Co. There will be no. goodwill if actualprofit is less than normal profit.

In method (iii ) goodwill is as per value of the business and is determined by the ratio of:

Estimated annual profit100,

Normal rate of return× The value of goodwill is the value of business less net assets

of the company. In goodwill determination, debentures are excluded. Fixed assets, less depreciationwritten off, + net working capital.

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ISO � 9000 SERIES QUALITYASSURANCE SYSTEM

Chapter

54

1. ISO – 9000 series quality assesment system was first introduced by EAC in Europe 1990s andEAC guidelines on the application of EN 45012 for quality assurance assessment entities indifferent countries accredited to few quality certifying authorities viz TuV, BvOi, RvC, DAR etc.ISO 9000 series standards are in six parts.

2. There are three ISO (International Standard Organisation) standards for quality assessmentdeveloped in Europe as follows:

EN ISO 9000 : 1994 (3 parts) – Part 1 and 2 are for QMS and QAS guidelines forappln. for ISO 9001 and part 3 for soft ware.

EN ISO 8402 : – quality management and quality assurance, vocabularyand scope.

EN ISO 9001 : 1994 – Model for quality assurance in design, development,production installation and servicing.

EN ISO 9002 : 1994 – Model for quality assurance is for selection and useand part 3 – production process installation andservices.

EN ISO 9003 : 1994 – Model for quality assurance in final inspection andtesting.

EN ISO 9004 : 1994 – Quality management and quality

(Part 1 and 2) system elements – Guidelines and equivalent.

EN ISO 10011 – Guidelines for lead assessors part 2

(Part 1, 2 and 3) and that part 1 and 3 give guidelines for qualitysystems.

NB. ISO 9000 series updated to 2000 from 1994

The corresponding equivalent Indian standard is IS14000 series viz IS14001, IS14002and IS14003 (1994). The British standard institute equivalent to ISO9000 is BS5750 1994(EN29000).

320

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EN ISO 10012 – QA requirement for measuring equipment.

EN ISO 3534 – is for statistics (SQC)

3. EAC Guidelines on the application of EN45012 (European standard) for bodies certifying suppliersquality system are applicable to entities doing assessment of a Co’s quality control systems indifferent countries must be accredited to European Nodal authorities Viz TuV, BvQi, RvC, DARetc., which gives its clearance. On the application of ISO –9001/9002 and ISO 9003 (as thecase may be), and the quality assessment organisation issues the ISO compliance certificate.

4. EAC guidelines in this regard has 29 clauses for compliance by a legal quality assessmentorganisation or a company accredited to TuV, BvQi, RvC, DAR etc. Each clause has EACinterpretation so that disputes are minimised between European certifying authority and the ISOcertificate issuing legal entity in a country accredited to the European certifying authority.

The quality assessment of a company is usually done by a qualified trained lead assessor andits team of assessors as per EAC guidelines. This also specifies the duration of time (mandays)on quality assessment depending on number of employees in the certified entity for initialassessment, subsequent annual visits and re-assessment visits. There are 39 sectors recordedas per NACE Rev. 1 for quality assurance and issue of ISO certificate by certifying bodiesaccredited to above Nodal bodies. For preventing misuse of ISO certificate or collusion betweencertifying organisation or a company and its client there are clauses in guidelines such asimpartiality, objectivity, reliability and expertise.

5. There are 10 steps for quality assurance and control for registration:

(i) Planning an audit.

(ii ) Preliminary audit.

(iii ) Quality survey manual.

(iv) Preregistration audit check list.

(v) Initial meeting with organisation head for the necessary information.

(vi) Auditing operation.

(vii) Final closing meeting with the organisation.

(viii ) Recording of discrepencies in auditing.

(ix) Audit reports.

(x) Corrective actions by the organisation and compliance. On going surveillance, is tocontinue.

6. Apart from quality assurance and control (TQC), there is a standard for quality managementsystem (QMS). The concept of quality requirement means customer's requirement first andevery time. Quality is to be measured, assessed and improve performance of business for whicha business organisation is divided into 7 lines of departments as below:

(i) Marketing.

(ii ) Selling.

(iii ) Design and Development.

(iv) Production Process.

(v) Purchasing.

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(vi) Finance and administration.

(vii ) After sales service.

The objects of QMS are:

(a) Improve customer satisfaction.

(b) Elimination of error and waste.

(c) Reduced operating cost.

(d) Increased motivation and commitment from employees.

(e) Increased profitability and competition.

7. ISO 9000 or its equivalents, IS–14000 and BS 5750 certification are mandatory requirementsfor export of product to Europe or USA. In addition FDD (US) clearance for export of Foodand Pharma products.

8. Upto 1995, 150 countries out of the then 178 UN member nations, had adopted ISO–9000 seriesof quality controls. Upto end 1994–100 Indian company have obtained ISO quality certificates.

9. Application clauses of ISO–9000 series

Applicable clauses ISO–9001 ISO–9002 ISO–9003

(1) (2) (3) (4)

Management and responsibility. 4.1 4.1 4.1

Quality system 4.2 4.2 4.2

Contract review 4.3 4.3 –

Design control 4.4 – –

Document control 4.5 4.4 4.3

Purchaser supplied Product. 4.7 4.6 –

Purchasing 4.6 4.7 –

Product identification and traceability 4.8 4.7 4.4

Process control 4.9 4.8 –

Inspection and testing 4.11 4.10 4.6

Inspection and Test status 4.12 4.11 4.7

Control of nonconforming product. 4.13 4.12 4.8

Corrective action 4.14 4.13 –

Handling, Packing, Storage and delivery. 4.15 4.14 4.10

Internal quality audit 4.17 4.16 –

Training 4.18 4.17 4.11

Servicing 4.19 – –

Statistical techniques 4.20 4.18 4.12

10. Procedure for adopting ISO–9000 certification by a company requires (i) visit to a ISO certifiedcompany and walk through the factory, discuss with management and quality assurance manager

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ISO-9000 SERIES QUALITY ASSURANCE SYSTEM 323

and read through their quality survey manual (ii ) Fill up application form and covering letter asto which ISO standard to be adopted as well as questionaire (iii ) application fee and(iv) Explanatory notes. These items are to be sent to certifying organisation who is accreditedto EN Nodal agency. The questionaire covers vendor assessment in process inspection patroland final inspection, Training, Equipment, calibration, Policy Control Procedure, reviews, design,customer guarantees and failure records.

However, it is better to get a preliminary audit by a competent consultant before applying forISO certification, who will give its recommendation citing shortcomings in various areas as perISO requirements based on which top management can take appropriate actions if CEO hasindependent discretion. The areas of checks include initial audit, design of a system, establishmentof specification and preregistration checks.

11. PRELIMINARY AUDIT (APPLICABLE TO ISO–9001 TO 9003)(i) Specification of raw materials and parts supplied by vendors.

(ii ) Visit to suppliers company to evaluate the response to a trial enquiry over telephone.

(iii ) Visit along with sales staff of prospective customers had either purchased goods fromthe company or had goods delivered to them. This will reveal about reactions of purchasers andsupplier's system of recording of enquiries and mode of follow up action on sending the quotation.

This action will reveal how far in prelimary audit one has to cover to instal a quality managementsystem in case of a production/service company. The findings of preliminary audit may give startingobservations viz:

(a) Sales people spending too much time to draw up specification

(b) Lost orders through delayed enquiries.

(c) Incomplete specification from sales to factory.

(d) Rejects, deliberatily being delivered to customers.

(e) High wastage in shop floor.

(f) In-attention to production. dept’s functioning resulting in poor production rate.

(g) Short supply in delivery.

(h) Staff, blaming each other for problems or delaying.

(i) Delay in procurement of raw materials and consumables etc.

Quality Audit manual by approved certification organisation or company. The following aspectsare to be considered.

(i) Management Policy and Organisation, Points to be ProvedWhether clear written policy is in circulation throughout the company. Deptt for executing the

policy – Any defined policy on quality with responsibilities – Are there any verification steps andresponsibilities defined?

Any assigned authority,

Training programme existing.

(ii ) Design and Revision Control(applicable to ISO 9001/9002)

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– Any control system for design and revision.

– Criteria for design, viz safety, reliability, maintenance, review and any other – identified fordeficiency and contractual or brief.

– Does the system control all documentation including production procedures and end users.

– Manufacturing and design interface is controlled or not.

– Any approved system for revision or changes.

– System of security, back up etc., or other changes and updating and traceability.

– Whether all finished products covered by full specification with user instructions.

(iii ) Procurement (Applicable to ISO 9001/9002)– Whether supplier agreement system exists.

– Standards for specification, identified for all incoming materials.

– Any agreement on quality with suppliers.

– Management procedure.

– Performance record of materials supplied.

– Suppliers capacity to adopt ISO 9000.

– Whether EDI (electronic data interface) exist with suppliers or other documentation systems.

– Traceability and identification possible.

(iv ) Control Reviewing (Applicable to ISO 9001/9002)– Whether formal contract entered with customer or only customer brief.

– Advertising process constitutes a contract or brief.

– Whether promises are being met or not.

– Equipment and its capacity is capable to meet control requirements.

(v) Quality System (Applicable to ISO 9001/9002/9003)– Whether the quality system conforms with requirements of relevant standard.

– What are the written procedures, controls and audit.

(vi ) Documentation Control (Applicable to ISO 9001/9002/9003)– Whether quality control manual contains all aspects, including updated informations.– Does the quality manual include all documents with procedural manuals and working

instructions, duly controlled.

– Availability of all documents when needed.

12. PRODUCTION PROCESSThis varies according to production process in chemical, mechanical, electrical, food, packaging

fields etc., based on the sector, a check list is to be prepared which will consider the following aspect:

(a) Consider every item of appropriate standard on process, traceability and production.

(b) Make sure that complete documentation about procedures, drawings, parts list/drawingsuppliers, diagrams, instrument settings instructions, models/paterns and reference models etc., areavailable.

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ISO-9000 SERIES QUALITY ASSURANCE SYSTEM 325

(c) Ensure that all the appropriate instructions are kept on relevant places of manuals/units inplastic envelopes and put in each operation place.

(d) Specify what the supervisor or inspector will lookout on rounds of a production unit.

(e) Check whether all necessary or critical controls and inspection sites/sections (whereoperators are posted) are manned and documented properly.

(f) Final assembly line check system for passed (O.K), in doubt or failed has been provided.

13. INSPECTION AND TESTING (APPLICABLE TO ISO 9001/9002/9003)– Whether incoming raw materials, chemicals and others are being tested for which adequate

facilities are available.

– Is the out-of-specification material controlled.

– Whether traceability of off-specifications is possible at storage for samples.

– Whether Q.C. inspectors has authority to release or prevent release of materials passed orfailed.

– Whether there is system for procedural inspection or monitoring in accordance with qualityplan and documented procedure.

– Is corrective action halts faulty items, allowing avoidance of off-specification items ortowards removal of faults.

– Whether off-specification materials are identified, segregated and disposed off.

– Are the storage areas properly controlled.

– Is there any final inspection, dock inspection and Patrol inspection.

– Is the purchase order specification/aggrement specify final inspection.

– Whether inspectors have final say in rejecting off specification items as per inspection.

– What is done with segregated nonconforming materials–returning, rework, scrap ofnonconforming items.

– Whether re-worked materials are inspected.

14. INSPECTION, MEASURING AND TEST EQUIPMENT (APPLICABLE TO ISO9001/9002/9003)

– Check inventory of all testing instruments.

– Whether there is documented procedure for calibration.

– Are the reference standards traceable to external calibration which are in turn approved byan international laboratory.

– Whether maintenance system of instruments exist or is in planning stage.

– Is the equipment manual specifies maintenance schedule and duly labelled for frequency ofcheck or calibration.

– Whether the off-specification plans of equipment are controlled.

15. HANDLING, DELIVERY AND STORAGE (APPLICABLE TO ISO 9001/9002/9003)– Check for storage areas for storage of finished goods duly segregated for off-specification

materials and duly controlled.

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326 REFERENCE BOOK ON CHEMICAL ENGINEERING

– Whether above items are marked as per status.

– Whether handling methods can damage the product.

– Whether the finished/semi finished/product items can be subjected to theft or maliciousdamage.

– Items, controlled by final inspection, can be either accepted or returned/objection placedby customer on any fault by inspectors.

16. AUDITS– Whether any initial in house auditing or by consultant.

– Is the audit covered by a plan and procedure and corrective actions recommended byauditors or consultants.

– Whether top management reviews the audit results and implements recommendations.

17. TRAINING– Whether regular training or seminar attendance in vogue.

– All such training courses/seminars are fully documented.

– Is the responsibility to fix training or seminar attendance is clearly defined.

– Are the supervisors properly trained.

– Whether training materials like books, videos, charts and lecturers can be searched out forwhich clear control system should exist.

18. HOUSE KEEPING– What is the state of front garden or yard ?

– How are the lobby/reception desk area look ?

– Is the receptionist and telephone operator friendly and available ?

– Is the plant and equipment maintained ?

– Is the work place clean ?

– Whether toilets are clean and system exists.

– Whether scraps are properly dealt with.

– Whether the walls, floors, roofs are clean.

– How does the canteen look ? Clean and pleasant ?

19. Once the health of a company is determined, thus actual planning for audit starts, design of asystem, establishment of specification followed by checks of parameters of preregistrationchecks and submission of quality survey manual to the company who applied for relevant ISOcertificate. The steps involved are.

(a) Informed preliminary audit.

(b) Instal quality system.

(c) Final stage – Formal audit.

(d) Final stage – Inspection by certifying agency after rectification of short-comings.

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ISO-9000 SERIES QUALITY ASSURANCE SYSTEM 327

(e) In case of refusal of registration by certifying agency, the company is free to reapplywhenever the situation is corrected.

An ISO certified registard company cannot use certified Logo in products.

20. Post registration requirements involve 2–4 visits by certifying agency auditors or assessors forwhich the company has to give free access to them inside the installation, supply documentsand unhindered talk to the Co’s employees on quality matters in order to ascertain any irregularityor changes from survey manual. The validity of an ISO certificate is usually two years or so.

21. The qualification and experience of an audit team (evaluation team) is given in ISO–1001, part1 include training for ISO standards, assessment techniques, planning, organising, communicatingand overall management. The numbers of an audit team may comprise inside and outsideorganisation (to be audited) members and to be chaired by must be an experienced person. Theevaluation panel must meet ISO 10011– part 2 requirements and approved from nodal certifyingagency as well as specifies graduation in science/engineering and a minimum. of four years offull time practical experience and at least two years in quality assurance, prior to become anISO auditor. Addln. requirement of participation consists of 4 audits of 20 days duration each.The auditor must pass the testing of knowledge and skills by sitting in an exam, conducted bya national certification body, like Institute of Quality assurance (IQA) London U.K. or Nationalquality assurance (NQA) U.K. The total cost involved including fees to certifying agency, is high(approx. Rs. 10 million or below).

22. Total time period required including ISO 9000 certification for a big company by a certifyingagency is as below:

(i) Top management decision making --- 4 weeks

(ii ) Establish task force headed by a qualified auditor --- 4 ''

(iii ) Training in ISO series --- 10 ''

(iv) Evaluate existing systems --- 15 ''

(v) Upgradation of system procedures --- 8 ''

(vi) Prepare documentation --- 7 ''

(vii ) Appoint ISO certifying agency --- 4 ''

(viii ) Execute improved systems --- 8 ''

(ix) Evaluation by internal audit team --- 12 ''

(x) Make up of short fall --- 6 ''

(xi) Certification audit --- 10 ''

(xii) Revisit by certifying authority

for compliance checking --- 2 ''

Total : 92 weeks*

* For a medium sized organisation, it can be done at ½ of the total weeks.

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328 REFERENCE BOOK ON CHEMICAL ENGINEERING

CONVERSION FACTORS

Chapter

55

WEIGHT

1 lb = 16 oz = 7000 grains = 0.4536 kg = 453.6 gm

1 oz = 28.35 gms = 437.5 grains

1 oz (Troy) = 480 grains = 31.1035 gm

1 fl oz (U.K.) = 28.413 ml; 1 drachm = 1/8 fl. oz

1 fl oz (U.S.) = 29.574 ml

1 kg = 35.27 oz = 15432 grains = 2.2046 lb

1 ton (Br) = 1.016 metric ton = 20 cwt = 2240 lb

1 metric ton = 0.984 Br. ton = 10 quintal = 1000 kg.

1 c w t (hundred wt) = 112 lb = 50.8024 kg.

1 short ton (US) = 2000 lb = 907.2 kg.

1 lb/cft = 16.018 kg/m3

1 microgram = 10–6 gm

1 carat = 200 mg

1 lb force = 4.45 N

1 ton force = 9.96 kN

1 stone = 6.35 kg.

N.B. Troy system of weight is for precious metals/minerals.

PRESSURE – LOAD

1 lb per sq. inch (psi) = 27.71 inch water (62°F) = .0703 kg/cm2

= 2.036 in Hg = 51.715 Torr.

1 kg/cm2 = 14.22 psi = 0.9678 atm = 0.98 bar.

1 atm = 1.033 kg/cm2 = 14.696 psi = 760 mm Hg = 29.92 in Hg.

1 N = 1 kgm/sec2; 1 kp = 9.81 N = 33.93 ft of water

1 bar = 0.9875 atm. = 105 pascal

328

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CONVERSION FACTORS 329

1 1b/ft2 = 4.88 kg/m2

1 ton/sq.in (long ton) = 1.575 kg/mm2

(short ton) = 1.406 kg/mm2

1 kg/m2 = 0.205 lb/ft2

1 lb/sq.yd = 0.543 kg/m2

1 inch Hg (32°F) = 0.491 psi.

1 inch water (62°F) = 0.0361 psi

Absolute vacuum = 760 Torr/mm Hg.

1 Kilo pascal (kpa) = 1000 pascal (Pa) = 0.1013 × 10–3 atm

1. Mega Pascal (Mpa) = 106 pascal = 10 bar = 9.87 atm = 145 PSI

1 PSI = 6.89 kpa; 1 pascal = 10–3 kpa.

1 Torr = 1 mm Hg = 133.32 Pascal

kpa = atm

101.3kp = Kilopond = kilogramme force

LENGTH

1 Angstorm = 1/1000 of a micron

1 inch = 2.54 cm = 25.4 mm (or 25 mm)

1 cm = 0.3937 in

1 foot = 12 inch = 0.3048 m

1 yd = 3 ft = 0.9144 m

1 fathom = 2 yds = 1.8288 m

1 m = 3.28 ft = 39.37 in

1 mile = 8 furlong = 1760 yd = 1.61 km.

1 km = 0.621 mile = 1093.6 yd.

1 knot = 6080 ft = 1.8532 km.

1 micron = 10–6 mm

1 millimicron = 1 nm (Nanometer)

1 rod = 16.5 ft.

1 chain = 4 rods = 100 links = 66 ft.

l mile = 80 chains

1 furlong = 201 m; 1 mil = 1/1000 of inch

VOLUME

1 m3 = 35.315 cft = 264.2 U.S. gallons = 220 gallons (U.K.)

1 dm3 = 61.024 cu in

1 cubic in (Cu in) = 16.387 cm3

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330 REFERENCE BOOK ON CHEMICAL ENGINEERING

1 cc = 0.061 cu in = 10–3 lit.

1 cft = 0.02832 m3 = 28.32 lit = 6.23 gallons (U.K.)

= 7. 481 Gallons (U.S.)

1 cu yd = 0.7646 m3

1 register ton, U.K. = 100 cft = 2.832 m3

1 ocean ton (U.K.) = 40 cft = 1.328 m3

1 gallon (U.K.) = 4.543 lit. = 8 pints

1 gallon (U.S.) = 3.7854 lit. = 231 cu in

1 bushel (U.K.) = 36.3677 lit.

1 bushel (U.S.) = 35.24 lit. = 2150.42 cu in

1 barrel (U.K.) = 163.65 lit.

1 barrel (U.S.) = 158.99 lit.

1 lit = 61.03 cu in

1 hectolitre = 100 lit. = 0.1 m3

1 Br. Gallon water weighs 10 lbs

1 cft water weighs 62.3 lbs at 4°c

1 pint = 568 ml

1 acre ft = 1230 m3

AREA – PRESSURE

1 sq. in = 6.4516 cm2

1 sq. ft = 0.0929 m2

1 sq. yd = 0.836 m2

1 acre = 4840 sq yd = 43560 sq ft = 4047 m2

1 arc = 100 m2

1 sq. mile = 640 acre = 2.59 km2 = 258.998 hectare

1 m2 = 10.764 sq. ft.

1 cm2 = 0.1550 sq. in

1 hectare = 10000 m2 =2.47 acre

1 lb/cm2 = 0.07 kg/cm2

1 sq cm = 0.155 sq inch

1 kg/cm2 = 14.22 PSI = 0.98 bar

1 atm = 1.033 kg/cm2 = 14.7 PSI = 760 mm Hg.

1 sq inch = 6.452 sq. cm

1 m2 = 1550 sq inch

1 decimal = 449.275 sq. ft.

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CONVERSION FACTORS 331

TEMPERATURE

°K = tc + 273.15 (abs. temp)

°R = tf + 459.7 (abs. temp); °C = ft 32

1.8

−; °F = 1.8tc + 32

N.B. For temp difference, there is no need to add or substract 32

SPEED–QUANTITY

1 ft/min = 0.00508 m/s = 0.508 cm/s

1 ft/s = 0.3048 m/s = 30.48 cm/s

1 mph = 1.61 km/h = 0.447 m/s

1 kmph = 0.621 mph = 54.6 ft/min

1 knot per hr = 1.8532 km per hr.

1 rpm = 1 u/min; 1 NM3/day = 38.102 SCFD

1 gal (U.S.)/min = 0.227 m3/hr.

1 gal (U.K.)/min = 0.273 m3/h

1 lb/min = 27.216 kg/h

1 cfm or cuft/min = 28.317 lit/min = 1.7 m3/hr.

1 lb/Hph = 0.6077 kg/kwh = 0.4473 kg/psh.

1 gm/cm3 = 0.036 lb/in3

1NM3 = 1.055166 SM3; 1 SM3 = 36.11 SCF

HEAT

1 kj = 0.2389 Kcal

1 BTU = 0.252 Kcal

= 107.6 kg.m = 778 ft – lb = 1.055 kj

1 Kcal = 3.968 BTU = 4.186 kj

1 BTU/ft.hr °F = 1.488 kcal/m. hr. °C

1 G cal = 109 Kcal

1 Joule = 107 ergs = 9.48×10–4 BTU = 2.778 × 10–7 kwh = 0.102 kp.m

1 BTU/1b = 0.556 Kcal/kg

1 Kcal/Kg = 1.8 BTU/lb.

1 BTU/cft = 8.899 Kcal/m3

1 Kcal/m3 = 0.1125 BTU/cft

1 BTU/sft = 2.71 Kcal/m2

1 BTU/lb°F = 1 Kcal/kg°C

1 BTU/cft°F = 16.03 Kcal/kg°C

1 BTU/sq. in = 390.6 Kcal/m2

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332 REFERENCE BOOK ON CHEMICAL ENGINEERING

1 BTU/sq. in h°F = 703.08 Kcal/m2h°C

1 BTU/sq. ft h°F = 4.88 Kcal/m2h°C

1 BTU/sq. ft h°F = 0.1241 Kcal/mh°C

1 Therm = 105 BTU = 25.2 × 103 kcal = 29.31 kwh.

WORK – MOMENT – POWER

1 ft lb = 0.1383 Kgm = 0.001285 BTU

= 0.5121 × 10–6 Psh = 0.3241 Kcal

= 0.3766 × 10–6 kwh = 0.505 × 10–6 Hph.

1 w = 3.412 BTU/hr = 0.001 kj/s = 1 joules/s

1 yd lb = 0.415 kg m

1 in lb = 1.152 Kgcm

1 ft lb/s = 0.1383 Kgm/s = 2545 BTU/hr

= 0.00184 Ps

= 1.356 watt

1 HP = 550 ft lb/s

= 76.04 kgm/s

= 0.178 kcal/s = 0.746 kw

1 Newton (N) = 1 Kg. m/sec2 = 105 gmcm/sec2 = 105 dyne

1 Kgm = 7.233 ft – lb = 2.3438 Kcal = 0. 009296 B T U

1 H P = 0.746 KW

= 1.014 Psh

1 Boiler H. P. = 33475 B.T. U/hr

1 Hph = 1.014 Psh = 2680 Kj = 641 Kcal = 2545 B T U

= 0.746 Kwh.

1 kwh = 3412 B.T.U = 3600 kj = 860 kcal

1 kw = 1.34 H.P. = 14.316 kcal/min

= 1 kj/s = 3412 B.T.U/hr = 1.36 Ps

1 J = 1 Nm = 1 WS = 0.102 kpm

REFRIGERATION

1 Tr (Europe) = 211 Kj/min = 3.5167 K w = 50.4 Kcal/min

1 Tr (ton of refrigeration) U.S. = 200 B T U/min = 3024 Kcal/h

1 Br. ton of refrigeration = 3340 Kcal/hr.

= 220 B T U/min

1 B T U/Hph = 0.338 Kcal/Kwh

1 lb/h tr = 9 kg/hr per 1000 Kcal/hr.

1 lb/min tr = 0.15 kg/h per 1000 Kcal/h

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CONVERSION FACTORS 333

1 U.S. gal/min (tr) = 75 lit/h per 1000 Kcal/h

1 B T U/min (tr) = 5 Kcal/h per 1000 Kcal/h

1 HP/tr = 0.335 Ps per 1000 Kcal/h

Refrigeration process entail bringing ambient temp to B.P. of ethylene (170°K), low temperaturerange is from 170° K to m.p. of nitrogen and cryogenics temp is below 120°K.

VISCOSITY

1 poise = 0.1 Ns/m2 = 22

kps1.02 .10

m−

1 cp = 42

kps1.02 .10

m−

1 st = 10–4 m2/s = 100 mm2/s

1 cst = 10–6 m2/s

For absolute viscosity in metric unit, divide cp by 1000, (kg)

m.s

POWERS AND FRACTIONS OF 10Powers of 10 Symbol

1012 Tera ..... T

109 Giga ..... G

106 Mega ..... M

103 Kilo ..... K

102 Hecto ..... h

10 Deca ..... da

10–1 Deci ..... d

10–2 centi ..... c

10–3 milli ..... m

10–6 micron ..... µ10–9 nano ..... n

10–12 pico ..... p

1024 ..... Trillion (U.S. 1018 = Trillion)

1012 ..... Billion (U.S. 109 = Billion)

106 ..... million

105 ..... hundred thousand

Important Values

1 cv = 0.98632 H.P.

π = 3.142

Roman number

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334 REFERENCE BOOK ON CHEMICAL ENGINEERING

MM = 2000 gc = 9.806 m/sec2

M = 1000 1 Ps = 736 W

D = 500 1 Gauss = 1 line of magnetic

C = 100 induction/cm2

SI units (New) and RelationshipThe following chart contains a selection of SI–units (new units) as compared with those used

formerly. The relationship of both units to each other is also shown.

Old Unit New Unit SIName Designat. Name Designat Relationship

Angle, straight 1° = π/180 Rad; 1' = 1°/60;new degree g degree, minute, °,,,, 1" = 1'/60degree ° second, radiant rad 1rad = 1m/marc measure gon 1 g =1 gon; 1 gon = (π/200) rad

1 full angle = 2πrad

Mass kilogram kg 1 kg = 1000 gkilogram kg gram, tonne g,t, 1 t = 1 Mg = 1000 kg

Density kilogram/cubic kg/m3

kilogram/cubic kg/m3 meter kilogram/meter cubic decimeter kg/dm3 instead of spec. grav. or density

kilogram/liter kg/l

Force 1 p = 9.81.10–3Npond p Newton N 1 kp = 9.81 Nkilopond kp 1 N = 1 kgm/s2; 1 N = 0.10197 kp

Energy, work, 1 J = 1 Nm = 1 Ws = 0.102 kpmheat quantity 1 kW/h = 3.6 MJ 1 kW/h = 1.36 PS/herg erg 1 kpm = 9.81 Jcalone cal joule J 1 kcal = 4.2 kJhorse power hour ps/h kilowatt hour kW/h 1 kJ = 0.239 kcalkilopond meter kpm Newton meter Nm 1 PS/h = 0.736 kW/h

1 erg = 10–7J

Power kilowatt kw 1 PS = 736 Whorse power PS watt W 1 kW = 1.36 PSkilowatt kw joule/second J/s 1 W = 1 J/s

Refer to the following DIN standards for further details on SI–Units:

DIN 1301. DIN 1306, DIN 1314, DIN 1315, DIN 1341, DIN 1342, DIN 1345, DIN 66034, DIN 66035, DIN66036, DIN 66037.

Old Unit New unitName Designat Name Designat Relationship

Pressure (gases, liquid) 1 m WS = 0.098 barmeter water column m WC Newton/sq meter N/m2 1 mm Hg = 1.33 mbarmillimeter mercury column mm Hg = Pascal Pa 1 mm WS = 0.098 mbarmillimeter water colum mm WC Decanewton daN/cm2 1 atm = 1.013 bar

square

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CONVERSION FACTORS 335

physical atmosphere atm centimeter = bar bar 1 at = 0.981 bartechnical atmosphere at 1 torr = 1.33 mbartorr torr 1 mbar = 0.75 mm Hg

= 0.75 torr1 mbar = 10.197 mm WS1 bar = 1.02 at1 bar = 1.02 kp/cm2

1 bar = 0.987 atm1 N/m2 = 1 Pa = 10–5 bar

Stresses (mech.) 1 kp/cm2 = 0.0981 N/mm2

kilopond/square Newton/square meter N/m2 1 kp/mm2 = 9.81 N/mm2

centimeter kp/cm2 = Pascal Pa 1 N/mm2 = 10.2 kp/cm2

kilopond/square Newton/square 1 N/mm2 = 0.102 kp/mm2

millimeter kp/mm2 millimeter N/mm2 1 N/m2 = 1 Pa = 10–6 N/mm2

Dynamic viscosity Newton second/square Ns/m2 1 P = 0.1 Ns/m2 = 0.1 Paspoise P meter = Pascal second Pas

Kinematic viscosity square meter/second m2/s 1 St = 10–4 m2/sStokes St square millimeter /sec mm2/s 1 St = 100 mm2/s

Speed reciprocal minute min–1 Rev/min = 1/min = min–1

revolutions/minute rev/min reciprocal second s–1

Temperature Kelvin K 1°K = 1K = 1°C (Temp. Diff.)degree kelvin °K degree centigrade °C °K = –273.15 °C

1 K = –272.15 °C

Refer to the following DIN standards for further details on the SI units:

DIN 1301. DIN 1306. DIN 1314, DIN 1315, DIN 1341, DIN 1342, DIN 1345, DIN 66034, DIN 66035, DIN66036, DIN 66037.

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336 REFERENCE BOOK ON CHEMICAL ENGINEERING

A

Active carbon 75

– Manufacture 75

– Activation processes 75

– Properties 76

– Uses 77

Affinity laws for centrifugal pump 138

Alcohol 163

– Grades 163

– Proof of alcohol 163

– Products from 163

– Physical data for various alcohols –

(see T–11, vol. IIA)

Arsenic limit in water 125

– Range of removal 126

Aluminium prodn by electrolysis 210

Ammonia liq. production process 3

Analysis of sea salt and rock salt 48

Anodising 129

Anodic cleaning 129

Anode coating 129

A. P. John eqn. for dew point 257

Associated NG analysis 152

Atmospheric stability 260

Atmospheric temp above sea level 267

336

INDEX

B

Bacteriological contamination inraw water 124

Banned dyes 171

Beet sugar 229

– Process steps 229

Biogas plant (Domestic) 223

– Process 223

– CH4 generation rate 224

Bitumen 76

Blasting explosives 110

Bleaching by Kraft process 41

Bleaching by sulphite process 43

Blue water gas or water gas 146

– Generator 146

– Composition and cal. valueof B W G 147

Blast furnace gas 149

– Comp. and cal. value 149

– Cleaning 149

Benzene 162

– Products from 162

Betz co. eff. in wind power generation 134

B.O.D. definition 272

Boiler feed water pumps 237

– BFW pump, German regulation 237

– BFW pressure 237

– Power requirement of pump 237

Page 348: Reference Book on Chemical Engineering v. 1

INDEX 337

– Std. values of BFW 238

– Std. analysis of Boiler Water 239

CCarrier eqn. for dew point 257

Carbon black 179

– Grades and surface area 206

– CBFC specification 179

– Composition 180

– ASTM grades name 180

– Raw materials for various 180carbon blacks

Cellulosic fibres (see Rayon) 50

Chlor–Alkali cells 45

– Mercury cells 45

– Diaphragm cell 47

– Membrane cell 46

– Raw material (brine) soln.purification 48

– Equation for electrolysis 45

Chem. engg. operation in petroleumrefinery 71

– Cracking and reforming process 71

– Desulphurisation 73

Chimney

– Draught graph 67

Vapour pressure of paraffinichydrocarbon 68

Chlorination of water for disinfection 126

Chromite bricks, properties 104Chromite magnasite bricks properties 104

Centrifugal pump 135

– Total head 135

– Suction and disch. heads 135

– Characteristic curves 137

– N P S H 138

– Pump construction 138

– Output and efficiency 137

– Specific speed 139

– Losses in a pump 139

– Hydraulic balancing 139

– Impeller types 142

– Affinity laws 138

– Sketches for different suctionheads 140

– Sketches for different dischargeheads 141

Co conversion processes (ammonia) 5

– HT and LT 5

– C O D definition 272

Coating processes for 128

– Cathode coating 128

– Anode coating 129

– Resin electrodeposition 129

– Anodising 129

Coal gas 150

– H. T. coal carbonisation 150

– Composition and cal. value 151

– Colour index of dyes 171

– Colour wheel for complimentarycolours 222

– Graph for NCV of clean andraw coal 154

Cooling tower 212

– Types 212

– Natural draft 213

– Mechanical draft 213

– Spray pond 214

– Design criteria 213

– C. T. fan 214

– Performance Co-eff. 213

– Wet bulb temp. calculation 215

– Pressure drop in cir. water 215

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338 REFERENCE BOOK ON CHEMICAL ENGINEERING

– Make up water flow 216

– Rating of a cooling tower 216

– Blow down rate 215

– Treatment of purge water(blow down) 216

Condensate polishing 123

Conversion factors 328

SI units and relationship 334

Contracts for project 307

– Types 307

– Unit price/item rate 308

– Escalation/penalty clauses 308

– Cost ranges for installation ofa chem. plant and depreciation rates 306

Critical path method 254

Composition of clean dry air atsea level 261

Crude tar distillation 99

– Composition of crude tar 96

– Yield of fractions and temp. 97

– Pitch types and softening temp. 97

– Roadtar BS std. 97

– Refined products yield 98

– Plant and types 99

– Flow sheet for tar distillation 100

– Tar, Refined products 101

– Process 99

– pro-abid process 102

– Phenol recovery 102

– Naphthalene recovery 102

– Pure naphthalene 102

– Coumarene resin 101

– pitch for electrode binder 98

Crude oil refining 70

– Process 70

– Coaking process 73

Solubility curves for 241inorganic salts for

Crystallisation : AgNO3, KI

KNO3, Pb(NO3)2, NH4Cl, CuSO4

NaCl, KClO3, HgCl2, Na2SO41OH2O

Cooling conditions in industry and trade –

(see p103, Vol–IIA)

Cooling media data for CaCl2, NaCl –

Ethylene and methylene glycols

(see T130 to 133, Vol–IIA)

Calculation of calorific value ofsolid fuel 153

Graph for chimney draught calculation 67

Combustion calculation of NGfired boiler 62

DDemineralisation of water by

– ion exchangers 119

– selection of exchanger resins 119

– resin exchangers resin forDM water 121

– Flowsheet for demineralisationand silica removal 120

– Degasification of water 118

– Decarbonisation of water 122

– Partial demineralisation 122

– Mixed bed exchanger 122

– Condensate polishing 123

Depreciation rates 306

Desalination of sea water 123

Dry ice manufacture 181

Desulphurisation (catalyst) see p. 142Vol. II-A 107

Dew Point eqn. (Carrier) 257

Dyes and intermediates 170

– Types of dyes 170

– Dye intermediates 171

Page 350: Reference Book on Chemical Engineering v. 1

INDEX 339

– Dyeing Process 171

– Banned dyes 171

– Detonators 107

Detail project cost estimation 298

– Various cost heads 298

– Preliminary expenses 299

– Total civil cost factors 300

– P and M cost 300

– Misc. fixed cost 301

– Auxiliary utility costs 301

– Cost of effluent treatment plants 302including C. T. purge watertreatment

– Cost of oil pollution monitoringinstrument 304

– Cost of air pollution abatementscheme 304

– Sound pollution limits andmeasuring instrument 303

– Fees for know-how, drawingchecking, license etc. 304

– Project management chargesincluding statutory fees 304

– Erection charges 305

– Incidental charges 305

– Erection supervision charges 305

– Township, welfare and medicalexpenses 305

– Margin money on working capital 305

– Interest charges on borrowedmoney 306

– Commissioning expenses 363

– Escalation or contingencies 306

Dittus – Boltier eqns of heat transfer 27

Dielectric constants of textile glasses 259

Dew pt. – temp chart for flue gases 158

Dew pt.– temp chart for flue gaseswith SO2 158

EEffluent treatment methods for

industries 265

– Fertiliser plants 265

– D M plants 266

– Steam utility plants 266

– Sewage treatment 266

– Solid weste disposal 263

– Food industry waste 267– Cement industry 269– Porcelain industry waste 269– Iron and steel industry waste 269– Metal pickling waste 270– Electroplating industry 270– Soda ash plant waste 270

– Pharma industry waste 270

– Inorganic dye and colourant/intermediate plants waste 270

– Organic dye and intermediateindustry 271

– Pulp and paper industry waste 266– Dairy effluent treatment 271– Sugar mill effluent 271– Waste water with mercurry 271

– Controlling acts against waterand air EPA 1986 272

Effluent permissible limits for fertiliser plants

– Liq. effluents 267

– MINAS 267

– IS 2490–74 267

– Assam pollution control board 267

– Ambient air quality as per AirAct 1981 303

– Delay pond stipulation for treatedeffluents 272

– Public views on new industrialplant location and public hearingat SDO’s office 272

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– Air pollution causes 273

– Green house gases and ozonehole in Antarctica 260, 268

– Anti pollution measures for airpollution 273, 268

– Inversion of temp due toatmospheric unstability 260

– Monitoring stations for air pollution andwind velocity measurant/indication 304

– Suction air filters for air blowers/compressors 273

– Atmospheric temp above sea level 267

– Solar energy distribution on earth 260

Environment and Pollution, Air and Water 260

– Methods of control of liq effluents 261

– Chemical methods 261

– Biological methods 262

– Solid waste disposal 263

– Segregation of waste streams 263

Electroplating

– Faraday’s law 207

– Std. Oxdn–reduction potentialssee T–18 vol. IIA

– Rack plating 208

– Barrel plating 208

– Spot plating or brush plating 208

– Pulse plating 208

– Non electrolytic deposition 238

– Various plating processes –

– Gold plating 208

– Tin plating 209

– Cadmium plating 209

– Chromium plating 209

– Copper plating 209

– Bright gold deposit 210

– Pure Aluminium prodn. 210

– Other considerations in electroplating 211

– Cathode and anode Coating 211

– Evacuation of a vessel as a function of time 69

Electrophoresis 181

– separation of materials 181

Electrolytic chlorinator 183

Ethyl benzene, products from 165

Ethylene, products from 164

Ethylene oxide, products from 164

Expanded or foamed plastics 177

Explosives 107

– Classification 108

– Gaseous explosion and explosiondue to pr. vessel failures 107

– Detonation of an explosive 107

– Detonation velocity table 108

– Names of some primary explosives 109

– Secondary explosives for industrialuses and high explosives 108

– Properties of high explosives 109

– Plastic explosives 110

– Impact sensitivity of secondaryexplosives 109

– Functional groups in explonives 110

F

Fatty acids conc. in oils, fats and milk –(see Table 150 Vol–IIA)

Fertilisers 1

Ferro alloys 232

– Production processes 232

– Composition of ferro alloys 233

Fire fighting network 177

– Classes of fire (see T34 vol–II B) –

– underground fire water hydrantsystem 177

– Fire pump and booster pumps 177

– Slandby diesel fire pump 178

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INDEX 341

– Fire fighting accessories 178

– Foam fire installation 178

– Fire engine or tender 178

– Fire water storage, over head/surface reservoir 178

– TAC approval of fire water hydrantsystems 178

– Empty bag storage-auto sprinklersystem 178

Fire detection alarms 175

– Ionisation smoke detection chamber 175

– Photo electric cell for smokedetection 176

– Fusible alloy water sprayers 176

Float glass 179

– Pilkington float glass process 179

– Uses 179

Flocculants 195

– Inorganic 195

– Organic 195

– Trade names and manufacturers 195

– Testing Parametres for flocculants 196

– Industry wise use of flocculants 196

Flame retardants 174

– Names 174

– Physical action 174

– Application 174

Fluorescent or optical whitening agents 172

– Functions 172

– FWA nos. and R groups 172

– Material for bleaching, FWA no. 194

– LD50 limit 173

– Uses 173

Fouling factors for different cooling

– water for H. Es (see T63 Vol. IIA)

Furfural 282

– Properties 282

– Raw materials and Manufacture 282

– Handling and storage 284

– Uses 284

Foamed plastics and rubber 177

Fertiliser

– Types of inorganic fertilisers 1

– Danger criteria for fertilisers 2

– Raw materials for fertilisers production 3

– Brief process steps 3

– Detail process for ammonia from NG 4

– Process for raw gas (CO+H2) prodn.by partial oxdn. of fuel oil/LSHS 7

– CO2 removal processes comparison 9(UOP, and BASF)

– Uhde ammonia synthesis loop data 9

– Sp. consumption in ammonia plant(NGbased) and energy requirement 10

– Process data for Kellog reformingexchanger 10

– Ammonia synthesis and steamnetwork 11

– Associated NG analysis 17

– Urea plant–process brief 12

– Stamicarbon CO2 stripping process–urea 13

– Snam NH3 stripping process 14

– Flowsheet for Snam NH3+strippingprocess 15

– TEC’s ACES process for urea 15

– Montedison IDR urea process 16

– Specific consumptions comparisionin urea process 17

– Comparative statement on energyconsumption 18

– By product CO2 from ammonia plant 17

– Flowsheet for ammonia productionfrom NG and LSHS 6, 8

– Vap. press– temp. curve for ammonia 20

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– Viscosity of ammonia and ammoniavapour 21, 22

– Thermal conductivity of liq. ammonia 23

– Viscosity of urea aq. soln. 24

– Storage for Fertiliser 16

GGalvanic series of metals and graphite –

(see T-66 vol IIA)

Grog 106

Green strength 106

Glass and textile glass fibres 258

– Types of glasses and uses 258

– E glass 258

– C glass 258

– A glass 258

– E C R glass 258

– R glass 258

– D glass 258

– S glass 258

– ISO nos for textile filament 259

– Composition of glasses 259

– Use of textile glass fibres 259

– Dielectric constants of Tex glassesat 1 MHz 259

HHalons – fire extinguishing chemicals 175

– Types 175

– Characteristics 175

– Uses 175

– Toxicity 175

Heat exchangers

– Convection heat transfer 25

– Temp. difference, mean/LMTD 26

– Graph for LMTD determination 36

– Reynolds no, Prandtl no. andNusselt no.–convection 27

– Dittus – Boltier eqn. for film co–eff,heatingfluid–turbulent flow 27

– Heat transfer eqn. for forced convection,film co–eff. at perpendicular to banksof staggerd tubes 27

– Heat transfer eqn. for film co–efffor condensing vapours inhorizontal tubes 27

– Heat transfer eqn. for film co–efffor vertical tubes 27

– Overall heat transfer co–eff, formultipass heat exchangers 28

– Fouling factors and temp. appln.ranges 28

– Shell side/Tube side 26

– Bafflecut and baffle spacing 26

– Sketch for annular and segmental

cut baffles with symbols 58

– Types of heat transfer equipment 29

– Cascade flow coolers for gases 30

– Radiant flow heat transfer equation 35

– Mechanical codes for Heatexchanger construction 26

– Heat transfer by conduction 31

– Tube pitch and tube layout 30

– No. of tubes for triangular pitch 34

– Layout as a function of shelldiameter tube spacing 35

– Approx. overall heat transferco-eff. for common H.Es 32, 33

– Root–sum– square norms forheat transfer area selection 28

– Typical calculation of a shell and tubeheat exchanger (steam heater) inurea plant 55

– Nomograph for LMTD for H.Es 38

I

Insecticides or Pesticides 243

– Properties 243

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INDEX 343

– Classification 244

– Grades of insecticides 244

– Insecticides group A – Acaricides 244

– Insecticide group C – Molluscicides 246

– Pesticides group B – Insecticides 244

– Fumigants – Group D 247

– Fungicides – Group E 247

– Herbicides – Group F 248

– Slimicides – Group G 249

– Rodenticides – Group H 249

– Nematicides – Group I 249

– Banned pesticides 250

– Toxicity of pesticides nomenclature 250

– Solvents/emulsifier for pesticides 250

– Nonionic emulsifiers 251

– Cationic emulsifiers 251

– Anionic emulsifiers 251

– Solid inorganic emulsifiers 251

– Natural emulsifiers 251

– Additives and stabilisers forpesticides 251

– Criteria of selection of specific emulsifier 251

– HLB value of emulsifier (non–ionic) 252

– Wood insects 253

– Manufacture of neem (margosa)based pesticides 253

– Industrial and town gases 143

– Producer gas 143

– Wellman gas producer 143

– Coppee gas producer 144

– Composition and cal. value 144

– Comparison of composition

– Cal. value when different fuelmaterials are used 144

– Operation problems of gasgenerators 145

– Efficiency of producer gasgenerators 145

– Cleaning of producer gas 146

– Uses 145

– Slagging ash producer gasgenerators 146

– Water gas or blue water gas 146

– Composition and cal. value 147

– Uses of water gas 147

– Carburated water gas or town gas 147

– Petro fuel used – Diesel oil 147

– Composition and cal. value 148

– Uses 148

– Semiwater gas 148

– Generator operation 148

– Raw material used 148

– Composition and cal. value 148

– Cleaning of raw gas 149

– Use 149

– Blast furnace gas 149

– Composition and cal. value 149

– Cleaning of B.F. gas 149

– Coal gas 150

– Raw material specification 150

– Process of manufacture(H.T. coal carbonisation) 150

– Composition and Cal. value 151

– Analysis of coke 151

– Uses of coke 151

International paper sizes (see vol. II BT–31) –

Ionic load in water 124

Iron and steel industry development 182

Iron Oxide Pigments (synthetic) 167

– Processes of manufacture 167

– Properties 168

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– Uses as colouring material 169

– International spec. of iron oxide 169

ISO–9000 series quality assurancesystem 320

– Fields of application of EN ISO9000 series 320

– Corresponding BS and IndianStandard 320

– EAC guide lines on appln. ofEN 45012 321

– Nodal agencies for accreditation ofcertifying organisation 321

– Ten steps for quality assuranceand control for TQC 321

– Q M S – lines of departments 321

– Application clauses of ISO–9000series for TQC (ISO-9001,ISO-9002 and ISO-9003)for manufacturing cos. 322

– Preliminary procedure forISO–9000 certification 322

– Preliminary audit (check list) 323

– Submission of quality auditsurvey manual 322

– Installation of quality system andfinal audit 323

– Submission of final audit report tonodal agency for approval 323

– Post visit for survey andcompliance 327

– Appln. for formal registrationby co. to certifying agency 326

– Total time period reqd. forISO–9000 certification 327

– Qualification and experience bar ofauditors as per ISO–1001–Part 1 327

– Validity of ISO–9000 seriescertification 327

JJoules Law

– Joules cycle in gas tubines, –Open cycle gas turbine generator(see Vol. II P. 55) –

LL. N. G Production 159

– Pretreatment of NG 159

– NG liquefaction processes 159

– Base load and cascade processes 159

– Detail cascade liquefaction processusing methane propane andethylene as refrigerants 159

– Physical data of propane,ethylene and methane 159

– Flow sheet 160

– Volumetric refrigerating effect 161

– Storage of L N G (one shore) 161

– Other L N G (data) 161

Light reflection factors of paints(see T–78 in vol–IIA) –

Lime softening process byclariflocculator 116

MMagnetic filtration of water 124

Manganese dioxide 130

– Types of MnO2 130

– Spec. of activated MnO2 130

– Activated manganous ore process 130

– Chemical MnO2 130

– Sedemar process for CMD 131

– Electrolytic MnO2(EMD) 131

– Spec. of EMD 131

– Manufacture of EMD 132

– Uses of Manganese dioxides 132

– Chrome Magnesite bricks,properties 104

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INDEX 345

– Mullite bricks, properties, Magnesitebricks, properties 105

Mixed bed exchangers 122

Mineral wool – glass fibres types,properties 187

– Chemical analysis 188

Metal cleaning processes 128

– Metal degreasing by organicchemicals 128

– Acid pickling 128

– Comp. and process for pickling 128

– Compressor lube oil circuit (refr.) 128

– Compr. suction lines etc. cleaning

– Cathodic cleaning for non-ferrous items 129

– Anodic cleaning for ferrous items 129

– Anodising for Al items 129

NNatural gas liquefaction 159

– Cascade process for LNG 159

Neutral ion exchanger resins 122

– Energy consumption in Fertiliserplants 18

– Ammonia–urea complex 18

– Non-Carbonate hardness of water 113

Net calorific value of clean and raw coal (SeeT-70, Vol-II A)

Net colorific value of clean and raw coal 154

O

Optical whitening agents 172Oligomers 285Off shore oil transportation pipe line 242

P

Paints and Painting 217

– Purposes and painting, decorativeand protection 217

– Significance of painting 217

– Typical components of paints andlacquers 217

– Paint vehicles 217

– Pigment colours and types 218

– Hiding units of pigments 220

– Solvents 219

– Dryers 218

– Additives 219

– Appln. of paints 221

– Uses 221

– Lacquers 218, 219

– Synthetic resin paints 221

– Industrial paints, types 221

– Colour wheel 222

Pesticides

– Insecticides 243

Petroleum Refinery 70

– Refinery category 71

– Crude oil types 70

– Products from crude oil 70

– Brief Process steps 70

– Flowsheet for primary crudedistillation 72

– Chem. Engg. Operating system 71

– Cracking/Reforming Process 71, 72

– Coking Process 73

– Flowsheet for coking process 73

– Desulphurisation 73

– Lubricating oils 74

– Bitumen/Asphalt 74

Plasticity of refractory 106

– Phosphoric acid 198

– Rock Phosphate ores 198

– Analysis of rock Phosphate (Florida) 199

– Selection of rock phosphate oresand limits of ores 200

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346 REFERENCE BOOK ON CHEMICAL ENGINEERING

– Chemical reactions 198

– Conc. Sulphuric acid requirementand heat dissipitation 200

– Dihydrate and Monohydratephosphoric acid, CaSO4 limits 199

– Phosphoric acid manufacture(dihydrate) 199

– Digestor or Reactor 201

– Key Process parameters 202

– Parameters of crystal form ofdifferent processes 231

– Phosphoric acid sludge 233

– Hemihydrate process 202

– Hemihydrate-Dihydrate process 203

– Concentration and clarification ofphosphoric acid 203

– Super phosphoric acid, chemicalcomposition 204

– Material of construction 205– Speed of fluids/chemical factors 205– Analysis of single super-phosphate 205– TSP (46% P2O5) 206– Capital cost break-up 206

Phenol recovery by tar distillation 102

Porosity of refractory bricks 106

Phenol for disinfection 230

– Phenols types 230

– Phenols classification as per germicidalvalue 230

– Testing of phenols 230– Phenol co-eff. test as per BS 231– Names of manufacturing process 231– Toxicity 231– Waste water treatment for phenol

recovery 231

Polyethylene terephthalate resin 285

– Specification of PET (Food gradebottle) 287

– Manufacturing Process 285

– Recycle of PET bottles 287

Pigments, iron oxide 167

– Synthetic Iron oxide Pigments 167,manufacture 168

– International specification 169– Properties 168

Pulp and Paper 37

– Grades of paper 37

– Paper sizes 38

– Test parameters for paper 38

– Raw materials – soft wood andhard wood 38

– Non wood fibres for pulping 38

– Textile fibres for pulping 38

– Manufacturing process 39

– Kraft or sulphate process 39

– Sulfite process 42

– General steps for chemical pulping 39

– Bleaching of pulp 40

– Bleaching steps for Kraft pulping 41

– Pulp beating and filtration 41

– Chemical recovery of Kraft digestorliquor 41

– Chemical recovery of sulphitedigestor liquor 42

– Bleaching steps 43

– Mechanical Pulping process 43

– Deinking of waste paper 43

– Speciality paper 43

– Bamboo Pulp 43

– Bagasse and corn stalk pulp 44

– Paper making by Hollander machine 44

Plastics 190

– Types of plastics 190

– Physical properties of commonplastics (see T–165, Vol. II A) 191

– Density of plastics (see T–160,Vol. IIA) –

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INDEX 347

– Additives for plastics 191

– Antistatic agent in plastics 192

– Solvents for plastics (see T–101,Vol. II A) –

– Glass transition temp and M.P ofplastics (see T–163, Vol. II A)–Specific heat and thermalconductivity of plastics (see T–161, Vol. II A) –

– Linear thermal expansion of someplastics (see P 219, Vol. II A) –

– Burning characteristics of someplastics (see T– 162, Vol. IIA)–

– Outline of plastics manufacturingprocesses 193, 192

– Processes for polyethylenemanufacture 194

– Foamed plastics–manufacturingprocess 193

– Plastics fabrication machines 193

– Plastics materials for packaging 194, 193

Producer gas 143

Process equipment (selected design) 53

Pre requirements

– Various calculation formulae 63-65

– Sizing of a vapour–liquid separatorfor urea plant service 53

– Sizing of a steam heater in ureaplant 55

– Combustion calculation for NGfired boiler furnace 62

Project Financial Management 309

– Internal rate of return (IRR) 309

– Procedure for determining IRR/ NPVand cash flows 309, 314

– Cost-benefit analysis 310

– Pay back period 311

– Rate of return Vs cost of capital 311

– Reqd. rate of return (ROR) 311

– Profitability index (PI) 312

– Break even point (BEP) 312

– Cut-off point of cost of capital 313

– Return on capital employed (ROCE) 313

– Rate of return (ROR) and ROE 214

– Compound interest 314

– Simple interest 314

– Term loan 315

– Fund provision by D/E ratio 315

– Promoter's contribution 315

– Security margin on term loan 316

– Unsecured loan 316

– Secured loan 316

– Cash credit (on inventory) 316

– Chattel mortgage 317

– Trust receipt loan 317

– Ware house (field) loan 317

– Terminal ware house receipt loan 317

– Compensating balance 317

– Line credit 317

– Revolving credit 317

– Transaction loans 317

– Definitions of some financial terms 318

– Sketch for impingement type separatoras per Pastonisi 76

Equation for run-off rate of rainfall 63

Formula for bubble cap plant gasvelocity through triangularslot/cap 63

Bernoulli’s theorem for determinationof pumping head 64

Friction drop calculation usingFanning eqn. 64

Estimation of H. E area/volume ofa vessel for similar process asper rule of three 65

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Estimation of nozzle sizes ofequipment when similar plant'scapacity and nozzle size areknown 65

Six tenth rule calculation forcosting 65

Formula for steam jacket pressureof pipe line when inner pipematerial data and workingpressure are known 66

Process evaluation of a chem. plant 228

– Preliminary check list 228

– Capacity checks of limitingequipment 288

– Material and Heat balance checks 288

– Utility balance and steam networkchecks 289

– Cooling water balance and C. T.heat load 289

– Process checks 292– Design checks 291– Instrument air and auxiliary air

spec. 290

– Basic site data sent to designeras per agreement 338

– Process control system provided 293– Whether pneumatic, electronic or

DCS 296

– Pollution (Water and air) to be tackledand quantified by designer 341

– Waste water treatment scope bydesigner or client 290 and 293

– CPCB and SPCB pollution (airand water) limits applicable fordischarges 290

– Graph for vessel evacuation time 80

– Graph for chimney height 78

– Statutory clearances 290

– Instrumentation and centralcontrol room 293

– Plant operating safety 291

R

Rayon 50

– Cotton linters as raw materials 50

– Processes for manufacture 50

– Viscose process 50

– Cellulose acetate process 52

– Cuperammonium process 51

– Cellulose nitrate process 52

Refrigeration 78

– Types of refrigeration process 78

– Vapour compression 78

– Absorption refrigeration 82

– Co-efficent of performances ofrefrigarants 78

– Types of refrigerant and R no. 78

– Application of refrigerants withtemp ranges (see table 120Vol. IIA) 91

– Alternate refrigerants in place ofHFCs and CFCs volumetricrefrigent effect 81

– Environmental hazards and TLVsfor refrigerants 81

– Units of refrigeration 82

– Heat pump typical output of heat 82

– Physical properties of commonrefrigerants 85

– Discharge temp. in single stageammonia compressor 86

– Procedures for measuringrefrigeration capacity 91

– Lubricating oils refrigeration(DIN 51503) 93

– Properties of lube oils 94

– Sec. cooling liquids as perevaporating temp. (See T-127Vol. IIA) –

– Vap. compression circuit 79

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INDEX 349

– Layout of vap. compressionrefrigeration system 80

– Layout of absorption refrigerationsystem 83

– Vapour press.– temp curves forrefrigerants 90

– Power requirement in refri. plantusing reciprocating compressor 86

– Power consumption in single stageabsorption refri. system for100,000 Kcal/hr cooling load 87, 88

Refractory bricks 103

– Types 103

– Properties (B. D., Porosity) temp.and uses of refractory bricks 106

– Silica bricks 103

– Dolomite bricks 103

– Chromite bricks 104

– Chrome magnesite bricks 104

– Alumino Silicate bricks 104

– Silimanite bricks 104

– Alumina bricks 104

– High Alumina bricks 104

– Magnesite bricks 105

– Fire clay bricks 105

– Mullite bricks 105

– Thermal expn. of refractory bricks 105

– Sizes of refractory bricks 106

– Thermal conductivity of refractorybricks –

(see T 106, Vol-II A)

– Green strength 106

– Porosity 106

– Plasticity 106

– Eqn. for modulus of rupture 106

– Mechanical properties of refractorybricks (see T 107, Vol. II A) –

Riot chemicals 110

Road Tar 97

Rock wool 187

– Raw materials 188

– Composition of mineral fibres 188

– Chemical analysis of Rock wooland glass wool 188

– Outlines of manufacturing process 188

– Physical properties 189

– Use (insulating material) 187, 189

– Thermal conductivity of mineralwool 187

Rubbers and expanded plastics 177

– Natural Rubber latex 176

– Rubber blends for tyre treads 177

– Glass transition temp, Tg (see T-163,Vol. IIA) 201

SSemi water gas 148

Solar energy 260

Sound decibel level 303

Sodium Chloride specification (Impurities) 48

SI–Metric units conversion factors 334

Synthetic iron oxide pigments 167

Strongly basic ion exchanger resins 121

Storage temp and R. H in cold storage(see T 129, Vol. II A ) –

Sugars 225

– Analysis of cane juice 225

– Manufacture of cane sugar 225

– Crushing of cane and extraction ofjuice 225

– Screening of juice 225

– Removal of suspended matter injuice 225

– Non sugar dispersoids in juice 225

– Clarification processes for rawsugar juice by liming processes 226

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– Cold liming 226

– Hot liming 227

– Fractional liming 227

– Fractional liming and double heatingprocess 227

– Carbonation process, single ordouble after liming 227

– Sulphitation process by SO2 228

– Evaporation of clarified juice forcrystallization 228

– Separation of crystals by centri-fugation and washing 228

– Drying of sugar crystals and directbagging 228

– By product molasses and use ofmolasses 228

– Comparison of different clarificationprocesses 228

– Manufacture of beet sugar 229

Sp. heat–true and mean of dry fluegases for hard Bituminous coal 155

Sp. heat –true and mean of dry fluegases for coke oven gas 155

Sp. heat –true and mean of dry fluegases for fuel oil 156

Sp. heat–true and mean of dry fluegases for natural gas 156

Sp. air and fluegas volumes–hardbituminous and soft coals 157

Sizing of vapour-liquid separator 53

T

Tar composition 99

– Coal Tar distillation process 97

– Refined product from tar distillation 101

– Refined products manf. process 101

– Tar distillation plant designers 99

– Pro–abid process 99

– Mazor differences in plants 99

– Coumarene resin recovery 101

– Phenol recovery 102

– Naphthalene recovery 102

– Pure naphthalene by chemicalprocess 102

– Flow sheet for Tar distillation 100

– Pitch types and softening points 97

– Road tar BS standard 97

Town gas or carburated water gas 147

U

Units of hardness in water (see T–96,Vol. II A) –

Urea prills spec. as per FPO 1969–70 –(see T– 137, Vol. II A)

Usual spec. of urea prills (F–G) –(see T–139, Vol. II A)

Urea Tech. grade spec. (IS–1781–71) –(see T–138, Vol. II A)

Urea Fertilizer prodn processes 12

V

Valves used in chemical industries 236

– Criteria of selection 236

– ASTM standards for materials 271

– Lubricant for valves used in O2service 236

– Vapour-liq separator-typical designas per Pastonisi (Vol. I and II) 53

Vegetable oils 275

– Names of Vegetable oils 275

– Properties of vegetable oils 275

– Oil seeds storage limitation 275

– Manufacturing process of ria bran oil 276

– Crude oil extraction by mech.expellers 275

– Flowsheet for vegetable oil refining 275

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INDEX 351

– Rice bran oil – solvent extraction 276

– Rice bran oil detail spec. 281

– Refining process for crude veg. oils 277

– Degumming process 278

– Alkali neutratiosation 278

– Bleaching operation 279

– Deodourisation process 279

– Hydrogenation of vegetable oils 281

– Smoke, flash and fire points ofveg oils –(see T–154, Vol II A)

– Fatty acids conc. in veg oils –(see T–156, vol–II A)

– Empirical eqns for physical data –of vegetable oils(see T–155, vol – II A)

Velocity of heat transfer media (HTM) –(see T–80, Vol – II A)

– Veg. oil specification(see T–158, Vol II A) –

– Flowsheet for solvent extractionprocess 277

V.P. of paraffinic hydrocarbons 67

WWater treatment 111

– Impurities in raw water 111

– pH value 112

– Alkalinity 112

– Titration results table 112

– Proforma with units for detailanalysis of water 113

– Permanent and Temporary hardness 114

– Water softening 114

– Quantity of chemicals reqd. 114

– Sedimantation of precipitates onchemical dosing by Ferric–Alum 115

– Settling velocity of particles inwater 115

– Softening process by clarifloc-culator 116

– Removal of iron and manganese saltsin water by aeration 116

– Demineralisation by ion exchangemethods 118

– Degasification of water 118

– Ion exchange resins exchanger forDM water 118

Water for boiler and other uses 119

– Selection of cation and anionexchanger resin 119

– Debasification resin (H exchanger) 121

– Dil Acid (HCL) reqd for regeneration(H exchanger) 121

– Block diagram for river watertreatment 133

– Ionic load 124

– Anion exchanger resin (OH resign) 121

– Partial dimineratlisation of waterexchanger 122

– Strongly basic and weekly basic anionexchanger dil. NaOH soln.

requirement 139

– Total demineralisation with silicaremoval for DM water for H.P. 122

– Flowsheet for total demineralisationof water 120

– Neutral exchanger resin (Naexchange) and its regenerationbrine solution required quantity 122

– Mixed bed exchangers 122

– Condensate polishing 123

– Zeolite resins 141

– Desalination of sea water byReverse osmosis 123

– Eqn. for reverse osmosis 123

Water treatment by magnetic filtration 124

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– limits for acceptable source ofraw water 124

– Settling ponds requirements forriver water with high turbidity 114

– EN 29000 std. for safe bottleddrinking water

– Arsenic removal process basedon As contamination 126

– IS14543–2003 for bottled drinkingwater specification 125

Water treatment basics 126